diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index dde9f15..57340eb 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -97,6 +97,8 @@ class PostsController < ApplicationController
       tags = Tag.normalise_tags(tag_names)
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      post.reload
       render json: post.as_json(include: { tags: { only: [:id, :category, :post_count],
                                                    methods: [:name, :has_wiki] } }),
              status: :created
@@ -136,6 +138,8 @@ class PostsController < ApplicationController
              Tag.normalise_tags(tag_names, with_tagme: false)
       tags = Tag.expand_parent_tags(tags)
       sync_post_tags!(post, tags)
+
+      post.reload
       json = post.as_json
       json['tags'] = build_tag_tree_for(post.tags)
       render json:, status: :ok
@@ -197,6 +201,8 @@ class PostsController < ApplicationController
   end
 
   def filter_posts_by_tags tag_names, match_type
+    tag_names = TagName.canonicalise(tag_names)
+
     posts = Post.joins(tags: :tag_name)
 
     if match_type == 'any'
diff --git a/backend/app/controllers/tags_controller.rb b/backend/app/controllers/tags_controller.rb
index 475f84e..d5e561f 100644
--- a/backend/app/controllers/tags_controller.rb
+++ b/backend/app/controllers/tags_controller.rb
@@ -16,12 +16,43 @@ class TagsController < ApplicationController
     q = params[:q].to_s.strip
     return render json: [] if q.blank?
 
-    tags = (Tag.joins(:tag_name).includes(:tag_name)
-            .where('(tags.category = ? AND tag_names.name LIKE ?) OR tag_names.name LIKE ?',
-                   'nico', "nico:#{ q }%", "#{ q }%")
-            .order(Arel.sql('post_count DESC, tag_names.name ASC'))
-            .limit(20))
-    render json: tags.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+    with_nico = !(params[:nico].to_s.strip.downcase.in?(['0', 'false', 'off', 'no']))
+
+    alias_rows =
+        TagName
+        .where('name LIKE ?', "#{ q }%")
+        .where.not(canonical_id: nil)
+        .pluck(:canonical_id, :name)
+
+    matched_alias_by_tag_name_id = { }
+    canonical_ids = []
+
+    alias_rows.each do |canonical_id, alias_name|
+      canonical_ids << canonical_id
+      matched_alias_by_tag_name_id[canonical_id] ||= alias_name
+    end
+
+    base = Tag.joins(:tag_name).includes(:tag_name)
+
+    canonical_hit =
+        base
+        .where(((with_nico ? '(tags.category = ? AND tag_names.name LIKE ?) OR ' : '') +
+                'tag_names.name LIKE ?'),
+               *(with_nico ? ['nico', "nico:#{ q }%"] : []), "#{ q }%")
+
+    tags =
+        if canonical_ids.present?
+          canonical_hit.or(base.where(tag_name_id: canonical_ids.uniq))
+        else
+          canonical_hit
+        end
+
+    tags = tags.order(Arel.sql('post_count DESC, tag_names.name')).limit(20).to_a
+
+    render json: tags.map { |tag|
+      tag.as_json(only: [:id, :category, :post_count], methods: [:name, :has_wiki])
+          .merge(matched_alias: matched_alias_by_tag_name_id[tag.tag_name_id])
+    }
   end
 
   def show
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 1bd0723..e25575f 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -8,8 +8,10 @@ class Post < ApplicationRecord
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :post
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
   has_many :tags, through: :active_post_tags
-  has_many :user_post_views, dependent: :destroy
-  has_many :post_similarities
+
+  has_many :user_post_views, dependent: :delete_all
+  has_many :post_similarities, dependent: :delete_all
+
   has_one_attached :thumbnail
 
   before_validation :normalise_url
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 491a0e3..e772e9c 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -3,53 +3,53 @@ class Tag < ApplicationRecord
     ;
   end
 
-  has_many :post_tags, dependent: :delete_all, inverse_of: :tag
+  has_many :post_tags, inverse_of: :tag
   has_many :active_post_tags, -> { kept }, class_name: 'PostTag', inverse_of: :tag
   has_many :post_tags_with_discarded, -> { with_discarded }, class_name: 'PostTag'
   has_many :posts, through: :active_post_tags
-  has_many :tag_aliases, dependent: :destroy
 
   has_many :nico_tag_relations, foreign_key: :nico_tag_id, dependent: :destroy
   has_many :linked_tags, through: :nico_tag_relations, source: :tag
 
-  has_many :reversed_nico_tag_relations, class_name: 'NicoTagRelation',
-                                         foreign_key: :tag_id,
-                                         dependent: :destroy
+  has_many :reversed_nico_tag_relations,
+           class_name: 'NicoTagRelation', foreign_key: :tag_id, dependent: :destroy
   has_many :linked_nico_tags, through: :reversed_nico_tag_relations, source: :nico_tag
 
   has_many :tag_implications, foreign_key: :parent_tag_id, dependent: :destroy
   has_many :children, through: :tag_implications, source: :tag
 
-  has_many :reversed_tag_implications, class_name: 'TagImplication',
-                                       foreign_key: :tag_id,
-                                       dependent: :destroy
+  has_many :reversed_tag_implications,
+           class_name: 'TagImplication', foreign_key: :tag_id, dependent: :destroy
   has_many :parents, through: :reversed_tag_implications, source: :parent_tag
 
+  has_many :tag_similarities, dependent: :delete_all
+
   belongs_to :tag_name
   delegate :name, to: :tag_name, allow_nil: true
   validates :tag_name, presence: true
 
-  enum :category, { deerjikist:  'deerjikist',
-                    meme:        'meme',
-                    character:   'character',
-                    general:     'general',
-                    material:    'material',
-                    nico:        'nico',
-                    meta:        'meta' }
+  enum :category, deerjikist:  'deerjikist',
+                  meme:        'meme',
+                  character:   'character',
+                  general:     'general',
+                  material:    'material',
+                  nico:        'nico',
+                  meta:        'meta'
 
   validates :category, presence: true, inclusion: { in: Tag.categories.keys }
 
   validate :nico_tag_name_must_start_with_nico
+  validate :tag_name_must_be_canonical
 
   scope :nico_tags, -> { where(category: :nico) }
 
   CATEGORY_PREFIXES = {
-      'gen:'  => 'general',
-      'djk:'  => 'deerjikist',
-      'meme:' => 'meme',
-      'chr:'  => 'character',
-      'mtr:'  => 'material',
-      'meta:' => 'meta' }.freeze
+      'gen:'  => :general,
+      'djk:'  => :deerjikist,
+      'meme:' => :meme,
+      'chr:'  => :character,
+      'mtr:'  => :material,
+      'meta:' => :meta }.freeze
 
   def name= val
     (self.tag_name ||= build_tag_name).name = val
@@ -60,11 +60,11 @@ class Tag < ApplicationRecord
   end
 
   def self.tagme
-    @tagme ||= find_or_create_by_tag_name!('タグ希望', category: 'meta')
+    @tagme ||= find_or_create_by_tag_name!('タグ希望', category: :meta)
   end
 
   def self.bot
-    @bot ||= find_or_create_by_tag_name!('bot操作', category: 'meta')
+    @bot ||= find_or_create_by_tag_name!('bot操作', category: :meta)
   end
 
   def self.normalise_tags tag_names, with_tagme: true, deny_nico: true
@@ -74,8 +74,8 @@ class Tag < ApplicationRecord
 
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.start_with?(p) } || ['', nil]
-      name = name.delete_prefix(pf)
-      find_or_create_by_tag_name!(name, category: (cat || 'general')).tap do |tag|
+      name = TagName.canonicalise(name.delete_prefix(pf)).first
+      find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         if cat && tag.category != cat
           tag.update!(category: cat)
         end
@@ -111,6 +111,8 @@ class Tag < ApplicationRecord
 
   def self.find_or_create_by_tag_name! name, category:
     tn = TagName.find_or_create_by!(name: name.to_s.strip)
+    tn = tn.canonical if tn.canonical_id?
+
     Tag.find_or_create_by!(tag_name_id: tn.id) do |t|
       t.category = category
     end
@@ -127,4 +129,10 @@ class Tag < ApplicationRecord
       errors.add :name, 'ニコニコ・タグの命名規則に反してゐます．'
     end
   end
+
+  def tag_name_must_be_canonical
+    if tag_name&.canonical_id?
+      errors.add :tag_name, 'tag_names へは実体を示す必要があります．'
+    end
+  end
 end
diff --git a/backend/app/models/tag_alias.rb b/backend/app/models/tag_alias.rb
deleted file mode 100644
index f695886..0000000
--- a/backend/app/models/tag_alias.rb
+++ /dev/null
@@ -1,6 +0,0 @@
-class TagAlias < ApplicationRecord
-  belongs_to :tag
-
-  validates :tag_id, presence: true
-  validates :name, presence: true, length: { maximum: 255 }, uniqueness: true
-end
diff --git a/backend/app/models/tag_name.rb b/backend/app/models/tag_name.rb
index 2efd022..225343d 100644
--- a/backend/app/models/tag_name.rb
+++ b/backend/app/models/tag_name.rb
@@ -6,4 +6,37 @@ class TagName < ApplicationRecord
   has_many :aliases, class_name: 'TagName', foreign_key: :canonical_id
 
   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
+
+  def self.canonicalise 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)
+
+    names.map { |name| tns[name]&.canonical&.name || name }.uniq
+  end
+
+  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?(':')
+      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．'
+    end
+  end
 end
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 07523b1..7ccdb52 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -30,6 +30,7 @@ RSpec.describe 'Posts API', type: :request do
     let!(:tag) { Tag.create!(tag_name:, category: "general") }
     let!(:tag_name2) { TagName.create!(name: 'unko') }
     let!(:tag2) { Tag.create!(tag_name: tag_name2, category: 'deerjikist') }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     let!(:hit_post) do
       Post.create!(uploaded_user: user, title: "hello spec world",
@@ -86,6 +87,25 @@ RSpec.describe 'Posts API', type: :request do
         end
       end
 
+      it "filters posts by q (hit case by alias)" do
+        get "/posts", params: { tags: "manko" }
+
+        expect(response).to have_http_status(:ok)
+        posts = json.fetch('posts')
+        ids = posts.map { |p| p['id'] }
+
+        expect(ids).to include(hit_post.id)
+        expect(ids).not_to include(miss_post.id)
+        expect(json['count']).to be_an(Integer)
+
+        posts.each do |p|
+          expect(p['tags']).to be_an(Array)
+          p['tags'].each do |t|
+            expect(t).to include('name', 'category', 'has_wiki')
+          end
+        end
+      end
+
       it "returns empty posts when nothing matches" do
         get "/posts", params: { tags: "no_such_keyword_12345" }
 
@@ -135,6 +155,7 @@ RSpec.describe 'Posts API', type: :request do
 
   describe 'POST /posts' do
     let(:member) { create(:user, :member) }
+    let!(:alias_tag_name) { TagName.create!(name: 'manko', canonical: tag_name) }
 
     it '401 when not logged in' do
       sign_out
@@ -167,6 +188,25 @@ RSpec.describe 'Posts API', type: :request do
       expect(json['tags'][0]).to have_key('name')
     end
 
+    it '201 and creates post + tags when member and tags have aliases' do
+      sign_in_as(member)
+
+      post '/posts', params: {
+        title: 'new post',
+        url: 'https://example.com/new',
+        tags: 'manko', # 既存タグ名を投げる
+        thumbnail: dummy_upload
+      }
+
+      expect(response).to have_http_status(:created)
+      expect(json).to include('id', 'title', 'url')
+
+      # tags が name を含むこと（API 側の serialization が正しいこと）
+      names = json.fetch('tags').map { |t| t['name'] }
+      expect(names).to include('spec_tag')
+      expect(names).not_to include('manko')
+    end
+
     context "when nico tag already exists in tags" do
       before do
         Tag.find_or_create_by!(tag_name: TagName.find_or_create_by!(name: 'nico:nico_tag'),
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 11cce46..c9aad4f 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -5,6 +5,7 @@ require 'rails_helper'
 RSpec.describe 'Tags API', type: :request do
   let!(:tn) { TagName.create!(name: 'spec_tag') }
   let!(:tag) { Tag.create!(tag_name: tn, category: 'general') }
+  let!(:alias_tn) { TagName.create!(name: 'unko', canonical: tn) }
 
   describe 'GET /tags' do
     it 'returns tags with name' do
@@ -56,6 +57,20 @@ RSpec.describe 'Tags API', type: :request do
 
       expect(json).to be_an(Array)
       expect(json.map { |t| t['name'] }).to include('spec_tag')
+      t = json.find { |t| t['name'] == 'spec_tag' }
+      expect(t).to have_key('matched_alias')
+      expect(t['matched_alias']).to be(nil)
+    end
+
+    it 'returns matching canonical tags by q with aliases' do
+      get '/tags/autocomplete', params: { q: 'unk' }
+
+      expect(response).to have_http_status(:ok)
+
+      expect(json).to be_an(Array)
+      expect(json.map { |t| t['name'] }).to include('spec_tag')
+      t = json.find { |t| t['name'] == 'spec_tag' }
+      expect(t['matched_alias']).to eq('unko')
     end
   end