diff --git a/backend/spec/models/tag_name_sanitisation_rule_spec.rb b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
index 558869e..dcecd06 100644
--- a/backend/spec/models/tag_name_sanitisation_rule_spec.rb
+++ b/backend/spec/models/tag_name_sanitisation_rule_spec.rb
@@ -62,7 +62,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
             name: 'foobar', language_code: 'en', tag_id: english.id)
         expect(primary_tag_name_for(japanese.reload, 'ja')).to have_attributes(
             name: 'foobar', language_code: 'ja', tag_id: japanese.id)
-        expect(english.reload.tag_name_id).to eq(english_name.id)
+        expect(primary_tag_name_for(english.reload, 'en')).to eq(english_name)
       end
     end
 
@@ -109,7 +109,7 @@ RSpec.describe TagNameSanitisationRule, type: :model do
         expect(existing.reload).to have_attributes(
             tag_id: source_tag.id, language_code: 'ja', primary_flg: true)
         expect(primary_tag_name_for(source_tag, 'ja')).to eq(existing)
-        expect(source_tag.reload.tag_name_id).to eq(existing.id)
+        expect(primary_tag_name_for(source_tag.reload, 'ja')).to eq(existing)
         expect(TagName.unscoped.exists?(source_tag_name_id)).to be(false)
       end
     end
diff --git a/backend/spec/models/tag_name_spec.rb b/backend/spec/models/tag_name_spec.rb
index 37107cc..aabcf0a 100644
--- a/backend/spec/models/tag_name_spec.rb
+++ b/backend/spec/models/tag_name_spec.rb
@@ -67,6 +67,22 @@ RSpec.describe TagName, type: :model do
   end
 
   describe '.canonicalise' do
+    it 'leaves detached aliases unchanged' do
+      create(:tag_name, :alias, name: 'detached_alias')
+
+      expect(described_class.canonicalise(Locale.nipponese, ['detached_alias']))
+          .to eq(['detached_alias'])
+    end
+
+    it 'leaves an alias unchanged when its language has no primary' do
+      tag = create(:tag, primary_name: '日本語のみ')
+      create(:tag_name, :alias, tag:, name: 'orphan_english_alias',
+                                language_code: 'en', script_code: 'Latn')
+
+      expect(described_class.canonicalise(locale, ['orphan_english_alias']))
+          .to eq(['orphan_english_alias'])
+    end
+
     it 'resolves the primary name of the alias language on the same tag' do
       tag = create(:tag, primary_name: '日本語正本')
       english_primary = create(:tag_name, tag:, name: 'english_primary',
diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index d900053..27c8565 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -331,6 +331,40 @@ RSpec.describe Tag, type: :model do
       Post.create!(url: 'https://example.com/posts/1', title: 'test post')
     end
 
+    context 'with names in multiple languages' do
+      include_context 'English locale'
+
+      it 'keeps the target primary and moves source names as aliases' do
+        english_primary = create(:tag_name, tag: target_tag,
+            name: 'target_english', language_code: 'en', script_code: 'Latn')
+        source_primary = create(:tag_name, tag: source_tag,
+            name: 'source_english', language_code: 'en', script_code: 'Latn')
+        source_alias = create(:tag_name, :alias, tag: source_tag,
+            name: 'source_english_alias', language_code: 'en', script_code: 'Latn')
+
+        described_class.merge_tags!(target_tag, [source_tag])
+
+        expect(primary_tag_name_for(target_tag.reload, 'en')).to eq(english_primary)
+        expect([source_primary.reload, source_alias.reload]).to all(have_attributes(
+            tag_id: target_tag.id, language_code: 'en', primary_flg: false))
+      end
+
+      it 'inherits a source primary when the target has no name in that language' do
+        source_primary = create(:tag_name, tag: source_tag,
+            name: 'inherited_english', language_code: 'en', script_code: 'Latn')
+        source_alias = create(:tag_name, :alias, tag: source_tag,
+            name: 'inherited_alias', language_code: 'en', script_code: 'Latn')
+
+        described_class.merge_tags!(target_tag, [source_tag])
+
+        expect(primary_tag_name_for(target_tag.reload, 'en')).to eq(source_primary)
+        expect(source_primary.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'en', primary_flg: true)
+        expect(source_alias.reload).to have_attributes(
+            tag_id: target_tag.id, language_code: 'en', primary_flg: false)
+      end
+    end
+
     context 'when merging a simple source tag' do
       let!(:source_post_tag) { PostTag.create!(post: post_record, tag: source_tag) }
 
@@ -388,13 +422,20 @@ RSpec.describe Tag, type: :model do
       expect(versions.pluck(:version_no, :event_type))
           .to eq([[1, 'create'], [2, 'discard']])
       expect(versions.first).to eq(original_version)
-      expect(versions.last).to have_attributes(
-          name: source_name, aliases: source_alias.name, created_by_user: user)
+      expect(versions.last.created_by_user).to eq(user)
+      expect(versions.last.names).to include(
+          hash_including('language_code' => 'ja', 'name' => source_name,
+                         'primary_flg' => true, 'auto_generated' => false),
+          hash_including('language_code' => 'ja', 'name' => source_alias.name,
+                         'primary_flg' => false, 'auto_generated' => false))
       expect(Tag.unscoped.exists?(source_tag.id)).to be(false)
 
       target_versions = target_tag.tag_versions.order(:version_no)
       expect(target_versions.pluck(:event_type)).to eq(['create', 'update'])
-      expect(target_versions.last.aliases.split).to contain_exactly('merge_alias', source_name)
+      target_aliases = target_versions.last.names.filter_map { |name|
+        name['name'] if name['language_code'] == 'ja' && !name['primary_flg']
+      }
+      expect(target_aliases).to contain_exactly('merge_alias', source_name)
     end
 
     it 'deletes source relationships while preserving unrelated relationships' do
diff --git a/backend/spec/requests/locale_write_paths_spec.rb b/backend/spec/requests/locale_write_paths_spec.rb
index 6c0ef8f..fa3b032 100644
--- a/backend/spec/requests/locale_write_paths_spec.rb
+++ b/backend/spec/requests/locale_write_paths_spec.rb
@@ -14,7 +14,6 @@ RSpec.describe 'Locale propagation on write paths', type: :request do
     expect(tag_name).to have_attributes(
         script_code: expected_locale.script_code, primary_flg: true)
     expect(tag_name.tag_id).to be_present
-    expect(tag_name.tag.tag_name_id).to eq(tag_name.id)
     tag_name.tag
   end
 
@@ -206,7 +205,6 @@ RSpec.describe 'Locale propagation on write paths', type: :request do
           .to have_attributes(
               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
diff --git a/backend/spec/requests/tag_versions_spec.rb b/backend/spec/requests/tag_versions_spec.rb
index 3a6383a..eebeca1 100644
--- a/backend/spec/requests/tag_versions_spec.rb
+++ b/backend/spec/requests/tag_versions_spec.rb
@@ -36,10 +36,11 @@ RSpec.describe 'TagVersions API', type: :request do
             category: category,
             deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
-            names: [{ language_code: 'ja', name: name, script_code: 'Jpan',
-                      primary_flg: true }] + Array(aliases).map { |alias_name|
+            names: [{ language_code: 'ja', name:, script_code: 'Jpan',
+                      primary_flg: true,
+                      auto_generated: false }] + Array(aliases).map { |alias_name|
               { language_code: 'ja', name: alias_name, script_code: 'Jpan',
-                primary_flg: false }
+                primary_flg: false, auto_generated: false }
             },
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 07478a0..be64b53 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -18,6 +18,18 @@ RSpec.describe 'Tags API', type: :request do
     response_tags.map { |t| t.fetch('name') }
   end
 
+  def version_primary_name(version, language_code)
+    version.names.find { |name|
+      name['language_code'] == language_code && name['primary_flg']
+    }.fetch('name')
+  end
+
+  def version_alias_names(version, language_code)
+    version.names.filter_map { |name|
+      name['name'] if name['language_code'] == language_code && !name['primary_flg']
+    }
+  end
+
   def dummy_material_upload(filename: 'dummy.png', type: 'image/png', body: 'dummy')
     Rack::Test::UploadedFile.new(StringIO.new(body), type, original_filename: filename)
   end
@@ -687,11 +699,11 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(versions.map(&:event_type)).to eq(['create', 'update'])
 
-        expect(versions.first.name).to eq('spec_tag')
+        expect(version_primary_name(versions.first, 'ja')).to eq('spec_tag')
         expect(versions.first.category).to eq('general')
-        expect(versions.first.aliases.split).to include('unko')
+        expect(version_alias_names(versions.first, 'ja')).to include('unko')
 
-        expect(versions.second.name).to eq('new_tag_name')
+        expect(version_primary_name(versions.second, 'ja')).to eq('new_tag_name')
         expect(versions.second.category).to eq('meme')
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
@@ -1261,13 +1273,13 @@ RSpec.describe 'Tags API', type: :request do
 
         expect(versions.map(&:event_type)).to eq(['create', 'update'])
 
-        expect(versions.first.name).to eq('spec_tag')
+        expect(version_primary_name(versions.first, 'ja')).to eq('spec_tag')
         expect(versions.first.category).to eq('general')
-        expect(versions.first.aliases.split).to include('unko')
+        expect(version_alias_names(versions.first, 'ja')).to include('unko')
 
-        expect(versions.second.name).to eq('put_versioned_tag')
+        expect(version_primary_name(versions.second, 'ja')).to eq('put_versioned_tag')
         expect(versions.second.category).to eq('meta')
-        expect(versions.second.aliases.split).to include('spec_tag')
+        expect(version_alias_names(versions.second, 'ja')).to include('spec_tag')
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
 
@@ -1307,8 +1319,8 @@ RSpec.describe 'Tags API', type: :request do
         version = tag.tag_versions.order(:version_no).last
 
         expect(version.event_type).to eq('update')
-        expect(version.name).to eq('spec_tag')
-        expect(version.aliases.split).to contain_exactly('put_roundtrip_b', 'unko')
+        expect(version_primary_name(version, 'ja')).to eq('spec_tag')
+        expect(version_alias_names(version, 'ja')).to contain_exactly('put_roundtrip_b', 'unko')
       end
 
       it 'parent tag の snapshot も作成する' do
@@ -1490,10 +1502,11 @@ RSpec.describe 'Tags API', type: :request do
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
         expect(old_owner_versions.first.event_type).to eq('create')
-        expect(old_owner_versions.first.aliases.split).to include('put_stolen_alias')
+        expect(version_alias_names(old_owner_versions.first, 'ja')).to include('put_stolen_alias')
 
         expect(old_owner_versions.second.event_type).to eq('update')
-        expect(old_owner_versions.second.aliases.split).not_to include('put_stolen_alias')
+        expect(version_alias_names(old_owner_versions.second, 'ja'))
+            .not_to include('put_stolen_alias')
       end
 
       it '別 tag の alias 名を rename で奪へる' do
@@ -1536,7 +1549,8 @@ RSpec.describe 'Tags API', type: :request do
         old_owner_versions = old_owner.tag_versions.order(:version_no)
 
         expect(old_owner_versions.last.event_type).to eq('update')
-        expect(old_owner_versions.last.aliases.split).not_to include('put_alias_collision_name')
+        expect(version_alias_names(old_owner_versions.last, 'ja'))
+            .not_to include('put_alias_collision_name')
         expect(wiki_page.reload.tag_name).to eq(primary_tag_name_for(tag, 'ja'))
       end
 
diff --git a/backend/spec/services/tag_version_recorder_spec.rb b/backend/spec/services/tag_version_recorder_spec.rb
index f97562c..c556d87 100644
--- a/backend/spec/services/tag_version_recorder_spec.rb
+++ b/backend/spec/services/tag_version_recorder_spec.rb
@@ -9,13 +9,10 @@ RSpec.describe TagVersionRecorder do
     Script.insert_all!([{ code: 'Latn', name: 'Latin', created_at: Time.current }])
     Locale.insert_all!([{ code: 'en', language_code: 'en', script_code: 'Latn',
                           name: 'English', created_at: Time.current }])
-    TagName.create!(tag:, language_code: 'ja', script_code: 'Jpan', name: '別名',
-                    primary_flg: false,
-                    canonical_id: tag.tag_name_id)
-    TagName.create!(tag:, language_code: 'en', script_code: 'Latn', name: 'English name',
-                    primary_flg: true)
-    TagName.create!(tag:, language_code: 'en', script_code: 'Latn', name: 'English alias',
-                    primary_flg: false)
+    create(:tag_name, :alias, tag:, name: '別名')
+    create(:tag_name, tag:, language_code: 'en', script_code: 'Latn', name: 'English name')
+    create(:tag_name, :alias, tag:, language_code: 'en', script_code: 'Latn',
+                              name: 'English alias')
   end
 
   it 'snapshots every language primary name and alias deterministically' do