diff --git a/backend/app/controllers/materials_controller.rb b/backend/app/controllers/materials_controller.rb
index 8bd5dae..837cb84 100644
--- a/backend/app/controllers/materials_controller.rb
+++ b/backend/app/controllers/materials_controller.rb
@@ -133,12 +133,14 @@ class MaterialsController < ApplicationController
     block = MaterialImportBlockMatcher.match_for_sha256(file_sha256)
     return render_material_import_block(block) if block
 
+    locale = resolve_locale!
+
     uploaded_blob = build_uploaded_material_blob!(file, file_sha256)
 
     begin
       Material.transaction do
         MaterialVersionRecorder.ensure_snapshot!(material, created_by_user: current_user)
-        tag = resolve_material_tag!(tag_name_raw)
+        tag = resolve_material_tag!(locale, tag_name_raw)
         material.assign_attributes(tag:, url:, updated_by_user: current_user)
         if uploaded_blob
           material.file.attach(uploaded_blob)
diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 228cb7b..4ca7a17 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -218,7 +218,7 @@ class PostsController < ApplicationController
     preflight = PostCreatePreflight.new(
         attributes: post_create_attributes,
         thumbnail: params[:thumbnail],
-        host: request.base_url).run
+        host: request.base_url).run(locale)
     return render json: dry_run_json(preflight) if bool?(:dry)
     if preflight[:existing_post_id].present?
       post = Post.new(url: preflight[:url])
@@ -273,13 +273,18 @@ class PostsController < ApplicationController
     return head :forbidden unless current_user.gte_member?
     return head :unsupported_media_type unless request.content_mime_type == Mime[:multipart_form]
     return head :payload_too_large if request.content_length.to_i > MAX_BULK_REQUEST_BYTES
+
+    locale = resolve_locale!
+
     posts = parse_bulk_posts_manifest
     thumbnails = parse_bulk_thumbnails(posts.length)
+
     result = PostBulkCreator.new(
         actor: current_user,
         posts:,
         thumbnails:,
-        host: request.base_url).run
+        host: request.base_url).run(locale)
+
     render json: result
   rescue JSON::ParserError
     render_bad_request 'posts manifest の JSON が不正です．'
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index ffa5696..e906737 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -406,10 +406,10 @@ class TagsController < ApplicationController
     return render_unprocessable_entity('カテゴリは必須です．', field: :category) if category.blank?
     return render_unprocessable_entity '廃止状態は必須です．', field: :deprecated unless params.key?(:deprecated)
 
-    return unless validate_tag_rename(tag, name)
-
     locale = resolve_locale!
 
+    return unless validate_tag_rename(locale, tag, name)
+
     alias_names = params[:aliases].to_s.split.uniq
     parent_names = params[:parent_tags].to_s.split.uniq
     deprecated = bool?(:deprecated)
@@ -455,6 +455,8 @@ class TagsController < ApplicationController
     return head :unauthorized unless current_user
     return head :forbidden unless current_user.gte_member?
 
+    locale = resolve_locale!
+
     name = params[:name].presence
     category = params[:category].presence
     deprecated_given = params.key?(:deprecated)
@@ -462,7 +464,7 @@ class TagsController < ApplicationController
 
     tag = Tag.find(params[:id])
 
-    return unless validate_tag_rename(tag, name)
+    return unless validate_tag_rename(locale, tag, name)
 
     if category.present? && category == 'nico'
       return render_unprocessable_entity 'ニコタグは変更できません．', field: :category
@@ -684,7 +686,7 @@ class TagsController < ApplicationController
         created_by_user:)
   end
 
-  def validate_tag_rename tag, name
+  def validate_tag_rename locale, tag, name
     return true if name.blank? || name == tag.name
 
     if tag.in?([Tag.tagme, Tag.bot, Tag.no_deerjikist, Tag.video, Tag.niconico])
@@ -692,9 +694,8 @@ class TagsController < ApplicationController
       return false
     end
 
-    target_tag_name = TagName.find_by(name:)
-    return true if target_tag_name.nil?
-    return true if target_tag_name.canonical_id?
+    target_tag_name = TagName.find_by(language_code: locale.language_code, name:)
+    return true unless target_tag_name&.primary_flg
 
     render_unprocessable_entity 'その名前は既に使はれてゐます．', field: :name
     false
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 8a60314..2648097 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -135,7 +135,7 @@ class Tag < ApplicationRecord
         raise SectionLiteralParseError.new(raw_name, raw_name)
       end
 
-      name = TagName.canonicalise(name).first
+      name = TagName.canonicalise(locale, name).first
 
       find_or_create_by_tag_name!(locale, name, category: (cat || :general)).tap do |tag|
         if deny_deprecated && tag.deprecated?
@@ -235,10 +235,7 @@ class Tag < ApplicationRecord
     end
 
     tag = tn.tag
-    if tag
-      tag.update!(tag_name_id: tn.id) if tag.tag_name_id != tn.id
-      return tag
-    end
+    return tag if tag
 
     tag = Tag.create!(tag_name: tn, category:)
     tn.update!(tag:)
@@ -279,6 +276,8 @@ class Tag < ApplicationRecord
         end
 
         TagVersioning.record!(source_tag, event_type: :discard, created_by_user:)
+        source_tag.tag_names.update_all(tag_id: source_tag.id, primary_key: false,
+                                        updated_at: Time.current)
         source_tag.destroy!
 
         source_tag_name.update_columns(canonical_id: target_tag.tag_name_id,
diff --git a/backend/app/models/tag_name.rb b/backend/app/models/tag_name.rb
index 82be505..91081ee 100644
--- a/backend/app/models/tag_name.rb
+++ b/backend/app/models/tag_name.rb
@@ -1,24 +1,36 @@
 class TagName < ApplicationRecord
+  belongs_to :language, foreign_key: :language_code, primary_key: :code
   belongs_to :tag, optional: true
   has_one :wiki_page
 
-  belongs_to :canonical, class_name: 'TagName', optional: true
-  has_many :aliases, class_name: 'TagName', foreign_key: :canonical_id
+  validates :name, presence: true,
+                   length: { maximum: 255 },
+                   uniqueness: { scope: :language_code }
 
-  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
-
-  validate :canonical_must_be_canonical
   validate :alias_name_must_not_have_prefix
-  validate :canonical_must_not_be_present_with_tag_or_wiki_page
+  validate :alias_must_not_have_wiki_page
   validate :name_must_be_sanitised
 
-  def self.canonicalise names
+  def primary? = primary_flg
+
+  def canonical = TagName.find_by(language:, tag:, primary_flg: true)
+  def aliases = TagName.where(language:, tag:, primary_flg: false)
+
+  def self.canonicalise locale, names
     names = Array(names).map { |n| n.to_s.strip }.reject(&:blank?)
     return [] if names.blank?
 
-    tns = TagName.includes(:canonical).where(name: names).index_by(&:name)
+    tns = TagName.where(language_code: locale.language_code, name: names).index_by(&:name)
 
-    names.map { |name| tns[name]&.canonical&.name || name }.uniq
+    names.map { |name|
+      if tns[name].primary_flg
+        name
+      else
+        TagName.find_by(language_code: locale.language_code,
+                        tag_id: tns[name].tag_id,
+                        primary_flg: true).name
+      end
+    }.uniq
   end
 
   def self.generate_name locale, tag, name
@@ -29,21 +41,15 @@ class TagName < ApplicationRecord
 
   private
 
-  def canonical_must_be_canonical
-    if canonical&.canonical_id?
-      errors.add :canonical, 'canonical は実体を示す必要があります．'
-    end
-  end
-
   def alias_name_must_not_have_prefix
-    if canonical_id? && name.to_s.include?(':')
+    if !(primary?) && name.to_s.include?(':')
       errors.add :name, 'エーリアス名にプレフィクスを含むことはできません．'
     end
   end
 
-  def canonical_must_not_be_present_with_tag_or_wiki_page
-    if canonical_id? && (tag || wiki_page)
-      errors.add :canonical, 'タグもしくは Wiki の参照がある名前はエーリアスになれません．'
+  def alias_must_not_have_wiki_page
+    if !(primary?) && wiki_page
+      errors.add :primary_flg, 'Wiki 参照がある名前はエーリアスになれません．'
     end
   end
 
diff --git a/backend/app/models/tag_name_sanitisation_rule.rb b/backend/app/models/tag_name_sanitisation_rule.rb
index 37cde5f..1086bbb 100644
--- a/backend/app/models/tag_name_sanitisation_rule.rb
+++ b/backend/app/models/tag_name_sanitisation_rule.rb
@@ -15,31 +15,38 @@ class TagNameSanitisationRule < ApplicationRecord
     end
 
     def apply!
-      TagName.find_each do |tn|
-        name = sanitise(tn.name)
-        next if name == tn.name
+      Language.find_each do |language|
+        TagName.where(language:).find_each do |tn|
+          name = sanitise(tn.name)
+          next if name == tn.name
 
-        TagName.transaction do
-          existing_tn = TagName.find_by(name:)
-          if existing_tn
-            existing_tn = existing_tn.canonical || existing_tn
-            next if existing_tn.id == tn.id
+          TagName.transaction do
+            existing_tn = TagName.find_by(language:, name:)
+            if existing_tn
+              unless existing_tn.primary_flg
+                existing_tn = TagName.find_by!(language:,
+                                               tag_id: existing_tn.tag_id,
+                                               primary_flg: true)
+              end
+              next if existing_tn.id == tn.id
 
-            existing_tag = Tag.find_by(tag_name_id: existing_tn.id)
-            source_tag = Tag.find_by(tag_name_id: tn.id)
+              existing_tag = existing_tn.tag
+              source_tag = tn.tag
 
-            if existing_tag
-              Tag.merge_tags!(existing_tag, source_tag) if tn.tag
-            elsif source_tag
-              source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+              if existing_tag
+                Tag.merge_tags!(existing_tag, source_tag) if tn.tag
+              elsif source_tag
+                source_tag.update_columns(tag_name_id: existing_tn.id, updated_at: Time.current)
+                existing_tn.update_columns(tag_id: source_tag.id, updated_at: Time.current)
+              end
+              tn.destroy!
+
+              next
             end
-            tn.destroy!
 
-            next
+            # TagName 側の自動サニタイズを回避
+            tn.update_columns(name:, updated_at: Time.current)
           end
-
-          # TagName 側の自動サニタイズを回避
-          tn.update_columns(name:, updated_at: Time.current)
         end
       end
     end
diff --git a/backend/app/services/post_create_plan.rb b/backend/app/services/post_create_plan.rb
index fedd574..6a0f9e6 100644
--- a/backend/app/services/post_create_plan.rb
+++ b/backend/app/services/post_create_plan.rb
@@ -8,13 +8,13 @@ class PostCreatePlan
     @existing_tags_by_name = nil
   end
 
-  def build!
-    direct_tag_specs, tag_sections = parse_direct_tag_specs
+  def build! locale
+    direct_tag_specs, tag_sections = parse_direct_tag_specs(locale)
     default_tag_specs = build_default_tag_specs(direct_tag_specs)
     snapshot_tag_specs = merge_tag_specs(direct_tag_specs + default_tag_specs)
     preload_existing_tags_by_name!(snapshot_tag_specs.map { _1[:name] })
     validate_new_tag_specs!(snapshot_tag_specs)
-    post_tag_specs = expand_parent_tag_specs(snapshot_tag_specs)
+    post_tag_specs = expand_parent_tag_specs(locale, snapshot_tag_specs)
     video_ms = normalise_video_ms(snapshot_tag_specs)
     validate_video_sections!(video_ms, tag_sections)
     parent_post_ids = normalise_parent_post_ids
@@ -42,13 +42,13 @@ class PostCreatePlan
 
   def tag_names = @attributes[:tags].to_s.split
 
-  def parse_direct_tag_specs
+  def parse_direct_tag_specs locale
     tag_sections = { }
     direct_tag_specs = []
 
     tag_names.each do |raw_name|
-      tag_name, category, sections = parse_raw_tag_name(raw_name)
-      existing_tag = existing_tags_by_name[tag_name]
+      tag_name, category, sections = parse_raw_tag_name(locale, raw_name)
+      existing_tag = existing_tags_by_name(locale)[tag_name]
       raise Tag::DeprecatedTagNormalisationError, [existing_tag.name] if existing_tag&.deprecated?
 
       direct_tag_specs << {
@@ -65,7 +65,7 @@ class PostCreatePlan
     [merge_tag_specs(direct_tag_specs), tag_sections]
   end
 
-  def parse_raw_tag_name raw_name
+  def parse_raw_tag_name locale, raw_name
     name = raw_name.to_s
     prefix, category =
         Tag::CATEGORY_PREFIXES.find {
@@ -74,7 +74,7 @@ class PostCreatePlan
     name = name.sub(/\A#{ prefix }/i, '')
 
     sections = []
-    while (match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/))
+    while match = name.match(/\A(\S*?)\[([^\[\]\s]*)-([^\[\]\s]*)\](\S*)\z/)
       name = "#{ match[1] }#{ match[4] }"
       next if match[2].empty? && match[3].empty?
 
@@ -87,17 +87,17 @@ class PostCreatePlan
       raise Tag::SectionLiteralParseError.new(raw_name, raw_name)
     end
 
-    [resolved_tag_name(name), category&.to_sym, sections]
+    [resolved_tag_name(locale, name), category&.to_sym, sections]
   end
 
-  def build_default_tag_specs direct_tag_specs
+  def build_default_tag_specs locale, direct_tag_specs
     default_tag_specs = []
     if direct_tag_specs.length < 10 && direct_tag_specs.none? { _1[:name] == TAGME_TAG_NAME }
       default_tag_specs << {
           name: TAGME_TAG_NAME,
           category: :meta }
     end
-    if direct_tag_specs.none? { deerjikist_tag_spec?(_1) }
+    if direct_tag_specs.none? { deerjikist_tag_spec?(locale, _1) }
       default_tag_specs << {
           name: NO_DEERJIKIST_TAG_NAME,
           category: :meta }
@@ -131,8 +131,10 @@ class PostCreatePlan
     raise ActiveRecord::RecordInvalid, post
   end
 
-  def expand_parent_tag_specs snapshot_tag_specs
-    existing_snapshot_tags = snapshot_tag_specs.filter_map { existing_tags_by_name[_1[:name]] }
+  def expand_parent_tag_specs locale, snapshot_tag_specs
+    existing_snapshot_tags = snapshot_tag_specs.filter_map do
+      existing_tags_by_name(locale)[_1[:name]]
+    end
     expanded_parent_specs =
         Tag.expand_parent_tags(existing_snapshot_tags)
            .reject(&:deprecated?)
@@ -156,33 +158,33 @@ class PostCreatePlan
     }.values.sort_by { _1[:name] }
   end
 
-  def existing_tags_by_name
+  def existing_tags_by_name locale
     @existing_tags_by_name ||= begin
-      names = tag_names.map { canonical_tag_name_without_sections(_1) }.uniq
+      names = tag_names.map { canonical_tag_name_without_sections(locale, _1) }.uniq
       Tag.joins(:tag_name).where(tag_names: { name: names }).index_by(&:name)
     end
   end
 
-  def preload_existing_tags_by_name! names
+  def preload_existing_tags_by_name! locale, names
     wanted_names = Array(names).map { _1.to_s }.reject(&:blank?).uniq
-    missing_names = wanted_names - existing_tags_by_name.keys
+    missing_names = wanted_names - existing_tags_by_name(locale).keys
     return if missing_names.empty?
 
-    existing_tags_by_name.merge!(
+    existing_tags_by_name(locale).merge!(
         Tag.joins(:tag_name)
            .where(tag_names: { name: missing_names })
            .index_by(&:name))
   end
 
-  def canonical_tag_name_without_sections raw_name
-    name, = parse_raw_tag_name(raw_name)
+  def canonical_tag_name_without_sections locale, raw_name
+    name, = parse_raw_tag_name(locale, raw_name)
     name
   end
 
-  def deerjikist_tag_spec? spec
+  def deerjikist_tag_spec? locale, spec
     return true if spec[:category] == :deerjikist
 
-    existing_tags_by_name[spec[:name]]&.deerjikist?
+    existing_tags_by_name(locale)[spec[:name]]&.deerjikist?
   end
 
   def normalise_parent_post_ids
@@ -260,10 +262,13 @@ class PostCreatePlan
     end
   end
 
-  def resolved_tag_name name
-    tag_name = TagName.includes(:canonical).find_by(name:)
-    return name if tag_name.nil?
-
-    (tag_name.canonical || tag_name).name
+  def resolved_tag_name locale, name
+    tag_name = TagName.find_by!(language_code: locale.language_code, name:)
+    unless tag_name.primary_flg
+      tag_name = TagName.find_by!(language_code: locale.language_code,
+                                  tag_id: tag_name.tag_id,
+                                  primary_flg: true)
+    end
+    tag_name.name
   end
 end
diff --git a/backend/app/services/post_creator.rb b/backend/app/services/post_creator.rb
index dbe4c89..b200901 100644
--- a/backend/app/services/post_creator.rb
+++ b/backend/app/services/post_creator.rb
@@ -21,14 +21,14 @@ class PostCreator
     ApplicationRecord.transaction do
       post.save!
       post.thumbnail.attach(thumbnail_attachment) if thumbnail_attachment.present?
-      snapshot_tags = planned_snapshot_tags
-      post_tags = planned_post_tags
-      sections = planned_sections
+      snapshot_tags = planned_snapshot_tags(locale)
+      post_tags = planned_post_tags(locale)
+      sections = planned_sections(locale)
       TagVersioning.record_tag_snapshots!(snapshot_tags, created_by_user: @actor)
       post.video_ms = planned_video_ms(locale)
       post.save!
       sync_post_tags!(post, post_tags, sections)
-      sync_parent_posts!(post, planned_parent_post_ids)
+      sync_parent_posts!(post, planned_parent_post_ids(locale))
       PostVersionRecorder.record!(post:, event_type: :create, created_by_user: @actor)
     end
     post
@@ -45,13 +45,15 @@ class PostCreator
         thumbnail_base: @attributes[:thumbnail_base].presence)
   end
 
-  def planned_snapshot_tags = planned_create_attributes[:snapshot_tags]
+  def planned_snapshot_tags(locale) = planned_create_attributes(locale)[:snapshot_tags]
 
-  def planned_post_tags = planned_create_attributes[:post_tags]
+  def planned_post_tags(locale) = planned_create_attributes(locale)[:post_tags]
 
-  def planned_sections = planned_create_attributes[:tag_sections]
+  def planned_sections(locale) = planned_create_attributes(locale)[:tag_sections]
 
-  def planned_parent_post_ids = planned_create_attributes[:normalised_parent_post_ids]
+  def planned_parent_post_ids locale
+    planned_create_attributes(locale)[:normalised_parent_post_ids]
+  end
 
   def planned_video_ms locale
     planned_create_attributes(locale)[:video_ms]
diff --git a/backend/spec/db/delete_discarded_tags_spec.rb b/backend/spec/db/delete_discarded_tags_spec.rb
index 3882e0d..6d6a533 100644
--- a/backend/spec/db/delete_discarded_tags_spec.rb
+++ b/backend/spec/db/delete_discarded_tags_spec.rb
@@ -11,6 +11,7 @@ RSpec.describe 'discarded tag cleanup migrations' do
   end
 
   context 'with legacy records' do
+    # Reproduce the historical schema required by these pre-multilingual migrations.
     self.use_transactional_tests = false
 
     before do
diff --git a/backend/spec/factories/tag_names.rb b/backend/spec/factories/tag_names.rb
index 4af5bcf..f4d6890 100644
--- a/backend/spec/factories/tag_names.rb
+++ b/backend/spec/factories/tag_names.rb
@@ -7,15 +7,6 @@ FactoryBot.define do
 
     trait :alias do
       primary_flg { false }
-
-      after(:create) do |tag_name|
-        owner = tag_name.canonical&.tag
-        raise ArgumentError, 'alias requires a canonical tag' unless owner
-
-        # The alias validation still rejects tag_id; its contract is tested separately.
-        tag_name.update_columns(tag_id: owner.id)
-        tag_name.association(:tag).reset
-      end
     end
   end
 end
diff --git a/backend/spec/models/locale_spec.rb b/backend/spec/models/locale_spec.rb
index d87bb56..a3b328e 100644
--- a/backend/spec/models/locale_spec.rb
+++ b/backend/spec/models/locale_spec.rb
@@ -27,10 +27,10 @@ RSpec.describe Locale, type: :model do
     expect(first.tag_names.find_by!(language_code: 'fr', primary_flg: true))
         .to have_attributes(name: 'name_from_generator', tag_id: first.id,
                             language_code: 'fr', script_code: 'Latn',
-                            primary_flg: true, canonical_id: nil)
+                            primary_flg: true)
     expect(second.tag_names.find_by!(language_code: 'fr', primary_flg: true))
         .to have_attributes(tag_id: second.id, language_code: 'fr',
-                            script_code: 'Latn', primary_flg: true, canonical_id: nil)
+                            script_code: 'Latn', primary_flg: true)
     expect(TagName.where(language_code: 'fr', primary_flg: true,
                          tag_id: [first.id, second.id]).count).to eq(2)
   end
@@ -53,13 +53,13 @@ RSpec.describe Locale, type: :model do
     prepare_french_reference!
     tag = create(:tag, name: 'alias_only_tag')
     alias_name = create(:tag_name, :alias, name: 'alias_fr',
-                                          canonical: tag.tag_name,
+                                          tag:,
                                           language_code: 'fr', script_code: 'Latn')
 
     create_french_locale!
 
     expect(alias_name.reload).to have_attributes(
-        canonical_id: tag.tag_name_id, tag_id: tag.id,
+        tag_id: tag.id,
         language_code: 'fr', script_code: 'Latn', primary_flg: false)
     generated = TagName.find_by!(tag_id: tag.id, language_code: 'fr', primary_flg: true)
     expect(generated).to have_attributes(tag_id: tag.id, language_code: 'fr',
diff --git a/backend/spec/models/tag_name_sanitisation_rule_spec.rb b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
index 6fb9929..50d0a10 100644
--- a/backend/spec/models/tag_name_sanitisation_rule_spec.rb
+++ b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
@@ -79,7 +79,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
       end
     end
 
-    context 'when a conflicting canonical tag_name exists' do
+    context 'when a conflicting primary tag name exists' do
       let!(:existing) { create(:tag_name, name: 'foobar') }
       let!(:source) do
         create(:tag_name, name: 'tmp').tap do |tn|
@@ -105,8 +105,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
 
       it 'moves the tag to the existing tag_name' do
         described_class.apply!
-        expected_tag_name_id = existing.canonical_id || existing.id
-        expect(source_tag.reload.tag_name_id).to eq(expected_tag_name_id)
+        expect(source_tag.reload.tag_name_id).to eq(existing.id)
         expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
       end
     end
@@ -114,7 +113,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
     context 'when the sanitised name is an alias of an existing tag' do
       let!(:existing_tag) { create(:tag) }
       let!(:alias_name) do
-        create(:tag_name, :alias, name: 'foobar', canonical: existing_tag.tag_name)
+        create(:tag_name, :alias, name: 'foobar', tag: existing_tag)
       end
       let!(:source) do
         create(:tag_name, name: 'tmp').tap do |tn|
@@ -122,11 +121,15 @@ RSpec.describe TagNameSanitisationRule, type: :model do
         end
       end
 
-      it 'deletes only the source and preserves the alias and its canonical tag' do
+      it 'deletes only the source and preserves the alias and its owning tag' do
         described_class.apply!
 
         expect(TagName.unscoped.exists?(source.id)).to be(false)
-        expect(alias_name.reload.canonical).to eq(existing_tag.tag_name)
+        expect(alias_name.reload).to have_attributes(
+            tag_id: existing_tag.id, language_code: 'ja', primary_flg: false)
+        expect(TagName.find_by!(tag_id: existing_tag.id,
+                                language_code: 'ja', primary_flg: true))
+            .to eq(existing_tag.tag_name)
         expect(Tag.find(existing_tag.id)).to eq(existing_tag)
       end
     end
diff --git a/backend/spec/models/tag_name_spec.rb b/backend/spec/models/tag_name_spec.rb
index 66aa120..b8e251f 100644
--- a/backend/spec/models/tag_name_spec.rb
+++ b/backend/spec/models/tag_name_spec.rb
@@ -32,37 +32,58 @@ RSpec.describe TagName, type: :model do
 
     expect(tag.reload.tag_name.reload.tag_id).to eq(tag.id)
     expect(tag.tag_name.tag).to eq(tag)
+    expect(described_class.find_by!(tag_id: tag.id, language_code: 'ja', primary_flg: true))
+        .to eq(tag.tag_name)
   end
 
-  it 'accepts an alias owned by the canonical tag' do
+  it 'persists an alias owned by the same tag as its primary name' do
     tag = create(:tag)
-    alias_name = build(:tag_name, name: 'valid_alias', canonical: tag.tag_name,
-                                 tag:, primary_flg: false)
+    alias_name = create(:tag_name, :alias, name: 'valid_alias', tag:)
 
-    expect(alias_name).to have_attributes(
-        canonical_id: tag.tag_name_id, tag_id: tag.id,
+    expect(alias_name.reload).to have_attributes(
+        tag_id: tag.id,
         primary_flg: false, language_code: 'ja')
-    expect(alias_name).to be_valid
+    primary = described_class.find_by!(tag_id: alias_name.tag_id,
+                                       language_code: alias_name.language_code,
+                                       primary_flg: true)
+    expect(primary).to eq(tag.tag_name)
   end
 
   describe '.canonicalise' do
+    it 'resolves the primary name of the alias language on the same tag' do
+      tag = create(:tag, name: '日本語正本')
+      english_primary = create(:tag_name, tag:, name: 'english_primary',
+                                          language_code: 'en', script_code: 'Latn')
+      english_alias = create(:tag_name, :alias, tag:, name: 'english_alias',
+                                                 language_code: 'en', script_code: 'Latn')
+      representative_id = tag.tag_name_id
+
+      primary = described_class.find_by!(tag_id: english_alias.tag_id,
+                                         language_code: english_alias.language_code,
+                                         primary_flg: true)
+
+      expect(primary).to eq(english_primary)
+      expect(described_class.canonicalise(locale, [english_alias.name]))
+          .to eq([english_primary.name])
+      expect(tag.reload.tag_name_id).to eq(representative_id)
+    end
+
     it 'resolves only aliases in the requested language' do
       japanese = create(:tag, name: 'japanese_canonical')
       english_name = create(:tag_name, name: 'english_canonical',
                                       language_code: 'en', script_code: 'Latn')
       english = create(:tag, tag_name: english_name)
       japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                 canonical: japanese.tag_name)
-      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
-                                                canonical: english_name,
+                                                 tag: japanese)
+      english_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                tag: english,
                                                 language_code: 'en', script_code: 'Latn')
-      english_alias.update_columns(name: 'shared_alias')
 
       expect(japanese_alias.reload).to have_attributes(
-          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          tag_id: japanese.id,
           primary_flg: false, language_code: 'ja')
       expect(english_alias.reload).to have_attributes(
-          canonical_id: english_name.id, tag_id: english.id,
+          tag_id: english.id,
           primary_flg: false, language_code: 'en')
       expect(described_class.canonicalise(locale, ['shared_alias']))
           .to eq(['english_canonical'])
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index e9683dd..13feb00 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -37,17 +37,16 @@ RSpec.describe Tag, type: :model do
                                       language_code: 'en', script_code: 'Latn')
       english = create(:tag, tag_name: english_name)
       japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                 canonical: japanese.tag_name)
-      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
-                                                canonical: english_name,
+                                                 tag: japanese)
+      english_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                                tag: english,
                                                 language_code: 'en', script_code: 'Latn')
-      english_alias.update_columns(name: 'shared_alias')
 
       expect(japanese_alias.reload).to have_attributes(
-          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          tag_id: japanese.id,
           primary_flg: false, language_code: 'ja')
       expect(english_alias.reload).to have_attributes(
-          canonical_id: english_name.id, tag_id: english.id,
+          tag_id: english.id,
           primary_flg: false, language_code: 'en')
       expect(described_class.normalise_tags!(
           english_locale, ['shared_alias'],
@@ -270,12 +269,12 @@ RSpec.describe Tag, type: :model do
       expect(tag.category).to eq('character')
     end
 
-    it 'reuses the canonical tag for an alias without changing its category' do
+    it 'reuses the owning tag for an alias without changing its category' do
       tag = create(:tag, category: :character)
       representative_id = tag.tag_name_id
-      alias_name = create(:tag_name, :alias, name: 'lookup_alias', canonical: tag.tag_name)
+      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
       expect(alias_name.reload).to have_attributes(
-          canonical_id: tag.tag_name_id, tag_id: tag.id,
+          tag_id: tag.id,
           primary_flg: false, language_code: 'ja')
       found = nil
 
@@ -289,14 +288,14 @@ RSpec.describe Tag, type: :model do
       expect(tag.reload.tag_name_id).to eq(representative_id)
     end
 
-    it 'reuses the canonical tag through another alias' do
+    it 'reuses the owning tag through another alias' do
       tag = create(:tag)
-      canonical = tag.tag_name
-      alias_name = create(:tag_name, :alias, name: 'lookup_alias', canonical:)
-      other_alias = create(:tag_name, :alias, name: 'lookup_other_alias', canonical:)
+      primary = tag.tag_name
+      alias_name = create(:tag_name, :alias, name: 'lookup_alias', tag:)
+      other_alias = create(:tag_name, :alias, name: 'lookup_other_alias', tag:)
 
       expect([alias_name.reload, other_alias.reload]).to all(have_attributes(
-          canonical_id: canonical.id, tag_id: tag.id,
+          tag_id: tag.id,
           primary_flg: false, language_code: 'ja'))
 
       expect {
@@ -305,7 +304,7 @@ RSpec.describe Tag, type: :model do
         expect(found).to eq(tag)
       }.to change(Tag, :count).by(0).and change(TagName, :count).by(0)
 
-      expect(tag.tag_name).to eq(canonical)
+      expect(tag.reload.tag_name).to eq(primary)
     end
   end
 
@@ -329,7 +328,8 @@ RSpec.describe Tag, type: :model do
         expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
         expect(target_link).to be_present
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -355,7 +355,8 @@ RSpec.describe Tag, type: :model do
         expect(target_post_tag.reload.sections).to contain_exactly(target_section)
 
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -363,7 +364,7 @@ RSpec.describe Tag, type: :model do
     it 'keeps source history and records the new target alias after deleting the source' do
       user = create_member_user!
       source_name = source_tag.name
-      source_alias = create(:tag_name, :alias, name: 'merge_alias', canonical: source_tag_name)
+      source_alias = create(:tag_name, :alias, name: 'merge_alias', tag: source_tag)
       TagVersioning.ensure_snapshot!(source_tag, created_by_user: user)
       original_version = source_tag.tag_versions.first
 
@@ -433,7 +434,8 @@ RSpec.describe Tag, type: :model do
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
         expect(PostTag.exists?(post: post_record, tag: source_tag)).to be(false)
         expect(target_link).to be_present
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -464,7 +466,8 @@ RSpec.describe Tag, type: :model do
         expect(target_link).to be_present
 
         expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
-        expect(source_tag_name.reload.canonical_id).to eq(target_tag.tag_name_id)
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'ja', primary_flg: false)
         expect(target_tag.reload.post_count).to eq(1)
       end
     end
@@ -493,7 +496,8 @@ RSpec.describe Tag, type: :model do
         }.to raise_error(ActiveRecord::RecordInvalid)
 
         expect(Tag.unscoped.exists?(earlier_source.id)).to be(true)
-        expect(earlier_name.reload.canonical_id).to be_nil
+        expect(earlier_name.reload).to have_attributes(
+            tag_id: earlier_source.id, language_code: 'ja', primary_flg: true)
         expect(TagVersion.where(tag_id: [earlier_source.id, source_tag.id, target_tag.id]))
             .to be_empty
         expect(Tag.unscoped.exists?(source_tag.id)).to be(true)
@@ -502,7 +506,8 @@ RSpec.describe Tag, type: :model do
         expect(source_post_tag.sections).to contain_exactly(source_section)
         expect(PostTag.find_by(post: post_record, tag: target_tag)).to be_nil
         expect(source_tag.reload.post_count).to eq(1)
-        expect(source_tag_name.reload.canonical_id).to be_nil
+        expect(source_tag_name.reload).to have_attributes(
+            tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
         expect(target_tag.reload.post_count).to eq(0)
       end
     end
diff --git a/backend/spec/requests/locale_write_paths_spec.rb b/backend/spec/requests/locale_write_paths_spec.rb
index f90a8c3..7d269dc 100644
--- a/backend/spec/requests/locale_write_paths_spec.rb
+++ b/backend/spec/requests/locale_write_paths_spec.rb
@@ -202,17 +202,19 @@ RSpec.describe 'Locale propagation on write paths', type: :request do
       expect(response).to have_http_status(:ok), response.body
       expect(TagName.find_by!(language_code: 'en', name: 'english_alias'))
           .to have_attributes(
-              script_code: 'Latn', canonical_id: english_name.id,
+              script_code: 'Latn',
               tag_id: tag.id, primary_flg: false, language_code: 'en')
       expect(tag.reload.tag_name_id).to eq(english_name.id)
+      primary = TagName.find_by!(tag_id: tag.id, language_code: 'en', primary_flg: true)
+      expect(primary).to have_attributes(name: 'english_original', script_code: 'Latn')
     end
 
     it 'does not take an alias from another language' do
       japanese = create(:tag, name: 'japanese_owner')
       japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                canonical: japanese.tag_name)
+                                                tag: japanese)
       expect(japanese_alias.reload).to have_attributes(
-          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          tag_id: japanese.id,
           primary_flg: false, language_code: 'ja')
 
       put "/tags/#{ tag.id }", params: {
@@ -221,12 +223,14 @@ RSpec.describe 'Locale propagation on write paths', type: :request do
 
       expect(response).to have_http_status(:ok), response.body
       expect(japanese_alias.reload).to have_attributes(
-          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          tag_id: japanese.id,
           primary_flg: false, language_code: 'ja')
       expect(TagName.find_by!(language_code: 'en', name: 'shared_alias'))
           .to have_attributes(
-              canonical_id: english_name.id, tag_id: tag.id,
+              tag_id: tag.id, script_code: 'Latn',
               primary_flg: false, language_code: 'en')
+      expect(TagName.where(name: 'shared_alias').pluck(:language_code, :tag_id))
+          .to contain_exactly(['ja', japanese.id], ['en', tag.id])
     end
   end
 end
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 585dacb..580271a 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -129,7 +129,7 @@ RSpec.describe 'Posts API', type: :request do
     let!(:tag) { create(:tag, tag_name:, category: :general) }
     let!(:tag_name2) { create(:tag_name, name: 'unko') }
     let!(:tag2) { create(:tag, tag_name: tag_name2, category: :deerjikist) }
-    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', canonical: tag_name) }
+    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
 
     let!(:hit_post) do
       Post.create!(uploaded_user: user, title: 'hello spec world',
@@ -351,7 +351,7 @@ RSpec.describe 'Posts API', type: :request do
       let!(:baz_tag) { create(:tag, tag_name: baz_tag_name, category: :general) }
 
       let!(:foo_alias_tag_name) do
-        create(:tag_name, :alias, name: 'not_spec_foo_alias', canonical: foo_tag_name)
+        create(:tag_name, :alias, name: 'not_spec_foo_alias', tag: foo_tag)
       end
 
       let!(:foo_only_post) do
@@ -854,7 +854,7 @@ RSpec.describe 'Posts API', type: :request do
             15.times.map do |i|
               tag_name = create(:tag_name, name: "show_query_tag_#{ i }")
               tag = create(:tag, tag_name:, category: :general)
-              create(:tag_name, :alias, name: "show_query_alias_#{ i }", canonical: tag_name)
+              create(:tag_name, :alias, name: "show_query_alias_#{ i }", tag:)
               PostTag.create!(post: post_record, tag:)
               tag
             end
@@ -999,7 +999,7 @@ RSpec.describe 'Posts API', type: :request do
 
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
-    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', canonical: tag_name) }
+    let!(:alias_tag_name) { create(:tag_name, :alias, name: 'manko', tag:) }
 
     it '401 when not logged in' do
       sign_out
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 26c1b52..8d10525 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -4,7 +4,7 @@ require 'rails_helper'
 RSpec.describe 'Tags API', type: :request do
   let!(:tn) { create(:tag_name, name: 'spec_tag') }
   let!(:tag) { create(:tag, tag_name: tn, category: :general) }
-  let!(:alias_tn) { create(:tag_name, :alias, name: 'unko', canonical: tn) }
+  let!(:alias_tn) { create(:tag_name, :alias, name: 'unko', tag:) }
   let!(:post) { Post.create!(url: 'https://example.com/unkounkounko') }
   let!(:post_tag) { PostTag.create!(post:, tag:) }
   let!(:tn2) { create(:tag_name, name: 'unknown') }
@@ -466,7 +466,7 @@ RSpec.describe 'Tags API', type: :request do
     it 'excludes external tags but preserves internal alias matches when nico is false' do
       internal = create(:tag, category: :general, name: 'switch_internal', post_count: 1)
       alias_target = create(:tag, category: :general, name: 'alias_target', post_count: 1)
-      create(:tag_name, :alias, name: 'switch_alias', canonical: alias_target.tag_name)
+      create(:tag_name, :alias, name: 'switch_alias', tag: alias_target)
       create(:external_tag, name: 'switch_external', post_count: 1)
 
       get '/tags/autocomplete', params: { q: 'switch', nico: '0' }
@@ -479,13 +479,13 @@ RSpec.describe 'Tags API', type: :request do
     end
 
     ['%', '_'].each do |wildcard|
-      it "treats #{ wildcard } literally for canonical, alias, and external names" do
+      it "treats #{ wildcard } literally for primary, alias, and external names" do
         literal = "literal#{ wildcard }match"
         create(:tag, category: :general, name: literal, post_count: 1)
         alias_target = create(
             :tag, category: :general, name: 'literal_alias_target', post_count: 1)
         create(:tag_name, :alias, name: "#{ literal }_alias",
-                                  canonical: alias_target.tag_name)
+                                  tag: alias_target)
         create(:external_tag, name: literal, post_count: 1)
         create(:tag, category: :general, name: 'literalXmatch', post_count: 2)
         create(:external_tag, name: 'literalXmatch', post_count: 2)
@@ -509,7 +509,7 @@ RSpec.describe 'Tags API', type: :request do
       expect(t['matched_alias']).to be(nil)
     end
 
-    it 'returns matching canonical tags by q with aliases' do
+    it 'returns matching primary tag names by q with aliases' do
       get '/tags/autocomplete', params: { q: 'unk' }
 
       expect(response).to have_http_status(:ok)
@@ -772,7 +772,8 @@ RSpec.describe 'Tags API', type: :request do
         }
 
         expect(response).to have_http_status(:ok)
-        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.reload.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'spec_tag'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
         patch "/tags/#{ tag.id }", params: { name: 'spec_tag' }
 
@@ -781,8 +782,10 @@ RSpec.describe 'Tags API', type: :request do
         tag.reload
 
         expect(tag.name).to eq('spec_tag')
-        expect(tag.tag_name.canonical_id).to be_nil
-        expect(TagName.find_by!(name: 'patch_roundtrip_target').canonical).to eq(tag.tag_name)
+        expect(tag.tag_name).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: true)
+        expect(TagName.find_by!(language_code: 'ja', name: 'patch_roundtrip_target'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
       end
 
       it '別 tag の正規名には変更できない' do
@@ -801,7 +804,8 @@ RSpec.describe 'Tags API', type: :request do
         )
 
         expect(tag.reload.name).to eq('spec_tag')
-        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('unko')
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .to contain_exactly('unko')
         expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
       end
 
@@ -1170,14 +1174,17 @@ RSpec.describe 'Tags API', type: :request do
         expect(tag.name).to eq('put_renamed_tag')
         expect(tag.category).to eq('meme')
 
-        expect(TagName.find_by(name: 'put_alias_a').canonical).to eq(tag.tag_name)
-        expect(TagName.find_by(name: 'put_alias_b').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_a'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
         old_name_alias = TagName.find_by(name: 'spec_tag')
         expect(old_name_alias).to be_present
-        expect(old_name_alias.canonical).to eq(tag.tag_name)
+        expect(old_name_alias).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
 
-        expect(alias_tn.reload.canonical).to be_nil
+        expect(alias_tn.reload.tag_id).to be_nil
 
         expect(tag.parents.map(&:name)).to contain_exactly(
           'put_kept_parent',
@@ -1212,7 +1219,8 @@ RSpec.describe 'Tags API', type: :request do
 
         tag.reload
 
-        expect(TagName.find_by(name: 'put_alias_self_test').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_alias_self_test'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
         expect(json['aliases']).to include('put_alias_self_test')
         expect(json['aliases']).not_to include('spec_tag')
       end
@@ -1283,10 +1291,14 @@ RSpec.describe 'Tags API', type: :request do
         tag.reload
 
         expect(tag.name).to eq('spec_tag')
-        expect(TagName.find_by!(name: 'put_roundtrip_b').canonical).to eq(tag.tag_name)
-        expect(tag.tag_name.aliases.map(&:name)).to contain_exactly('put_roundtrip_b', 'unko')
-        expect(tag.tag_name.aliases.map(&:name)).not_to include('spec_tag')
-        expect(alias_tn.reload.canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_roundtrip_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .to contain_exactly('put_roundtrip_b', 'unko')
+        expect(TagName.where(tag_id: tag.id, language_code: 'ja', primary_flg: false).pluck(:name))
+            .not_to include('spec_tag')
+        expect(alias_tn.reload).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
 
         version = tag.tag_versions.order(:version_no).last
 
@@ -1395,7 +1407,7 @@ RSpec.describe 'Tags API', type: :request do
         )
       end
 
-      it 'wiki を持つ tag を旧 alias へ戻しても wiki を新 canonical へ移す' do
+      it 'wiki を持つ tag を旧 alias へ戻しても wiki を新しい正本名へ移す' do
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: tag.tag_name,
@@ -1429,7 +1441,8 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(wiki_page.reload.tag_name).to eq(tag.tag_name)
         expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').wiki_page).to be_nil
-        expect(TagName.find_by!(name: 'put_wiki_roundtrip_b').canonical).to eq(tag.tag_name)
+        expect(TagName.find_by!(language_code: 'ja', name: 'put_wiki_roundtrip_b'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
 
         versions = wiki_page.wiki_versions.order(:version_no).last(2)
 
@@ -1443,9 +1456,11 @@ RSpec.describe 'Tags API', type: :request do
             category: :general)
         stolen_alias = create(:tag_name, :alias,
             name: 'put_stolen_alias',
-            canonical: old_owner.tag_name)
+            tag: old_owner)
 
-        expect(old_owner.tag_name.aliases.map(&:name)).to include('put_stolen_alias')
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .to include('put_stolen_alias')
 
         expect {
           put "/tags/#{ tag.id }", params: {
@@ -1461,8 +1476,11 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(response).to have_http_status(:ok)
 
-        expect(stolen_alias.reload.canonical).to eq(tag.tag_name)
-        expect(old_owner.reload.tag_name.aliases.map(&:name)).not_to include('put_stolen_alias')
+        expect(stolen_alias.reload).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: false)
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .not_to include('put_stolen_alias')
 
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
@@ -1479,7 +1497,7 @@ RSpec.describe 'Tags API', type: :request do
             category: :general)
         stolen_alias = create(:tag_name, :alias,
             name: 'put_alias_collision_name',
-            canonical: old_owner.tag_name)
+            tag: old_owner)
         wiki_page =
             Wiki::Commit.create_content!(
                 tag_name: tag.tag_name,
@@ -1502,9 +1520,13 @@ RSpec.describe 'Tags API', type: :request do
         stolen_alias.reload
 
         expect(tag.name).to eq('put_alias_collision_name')
-        expect(stolen_alias.canonical_id).to be_nil
-        expect(TagName.find_by!(name: 'spec_tag').canonical).to eq(tag.tag_name)
-        expect(old_owner.tag_name.aliases.map(&:name)).not_to include('put_alias_collision_name')
+        expect(stolen_alias).to have_attributes(
+            tag_id: tag.id, language_code: 'ja', primary_flg: true)
+        expect(TagName.find_by!(language_code: 'ja', name: 'spec_tag'))
+            .to have_attributes(tag_id: tag.id, primary_flg: false)
+        expect(TagName.where(tag_id: old_owner.id, language_code: 'ja',
+                              primary_flg: false).pluck(:name))
+            .not_to include('put_alias_collision_name')
 
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
diff --git a/backend/spec/services/post_create_plan_spec.rb b/backend/spec/services/post_create_plan_spec.rb
index e87b492..209def7 100644
--- a/backend/spec/services/post_create_plan_spec.rb
+++ b/backend/spec/services/post_create_plan_spec.rb
@@ -40,17 +40,16 @@ RSpec.describe PostCreatePlan do
                                       language_code: 'en', script_code: 'Latn')
       english = create(:tag, tag_name: english_name, category: :character)
       japanese_alias = create(:tag_name, :alias, name: 'shared_alias',
-                                                canonical: japanese.tag_name)
-      english_alias = create(:tag_name, :alias, name: 'temporary_alias',
-                                               canonical: english_name,
+                                                tag: japanese)
+      english_alias = create(:tag_name, :alias, name: 'shared_alias',
+                                               tag: english,
                                                language_code: 'en', script_code: 'Latn')
-      english_alias.update_columns(name: 'shared_alias')
 
       expect(japanese_alias.reload).to have_attributes(
-          canonical_id: japanese.tag_name_id, tag_id: japanese.id,
+          tag_id: japanese.id,
           primary_flg: false, language_code: 'ja')
       expect(english_alias.reload).to have_attributes(
-          canonical_id: english_name.id, tag_id: english.id,
+          tag_id: english.id,
           primary_flg: false, language_code: 'en')
 
       plan = described_class.new(attributes: { tags: 'shared_alias' }).build!(locale)
@@ -79,9 +78,9 @@ RSpec.describe PostCreatePlan do
     expect([TagName.count, Tag.count]).to eq(counts)
   end
 
-  it 'resolves aliases and keeps tag sections separate from canonical names' do
-    canonical = create_tag!('虹夏', :character)
-    create(:tag_name, :alias, name: 'にじか', canonical: canonical.tag_name)
+  it 'resolves aliases and keeps tag sections separate from primary names' do
+    tag = create_tag!('虹夏', :character)
+    create(:tag_name, :alias, name: 'にじか', tag:)
     create_tag!('動画', :meta)
 
     plan = described_class.new(