diff --git a/backend/spec/models/tag_spec.rb b/backend/spec/models/tag_spec.rb
index a6d14fd..014cdde 100644
--- a/backend/spec/models/tag_spec.rb
+++ b/backend/spec/models/tag_spec.rb
@@ -1,6 +1,79 @@
 require 'rails_helper'
 
 RSpec.describe Tag, type: :model do
+  describe '.normalise_tags!' do
+    it 'rejects deprecated tags when deny_deprecated is enabled' do
+      tag_name = TagName.create!(name: 'normalise deprecated tag')
+      deprecated_tag = Tag.create!(
+        tag_name:,
+        category: :general,
+        deprecated_at: 1.day.from_now
+      )
+
+      expect {
+        described_class.normalise_tags!(
+          [deprecated_tag.name],
+          deny_deprecated: true
+        )
+      }.to raise_error(Tag::DeprecatedTagNormalisationError) { |error|
+        expect(error.tag_names).to eq([deprecated_tag.name])
+      }
+    end
+  end
+
+  describe '.expand_parent_tags' do
+    it 'expands through multiple deprecated parents to an active ancestor' do
+      child = create(:tag, name: 'expand_child')
+      deprecated_parent = create(
+        :tag,
+        name: 'expand_deprecated_parent',
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = create(
+        :tag,
+        name: 'expand_deprecated_grandparent',
+        deprecated_at: Time.current
+      )
+      active_ancestor = create(:tag, name: 'expand_active_ancestor')
+      TagImplication.create!(tag: child, parent_tag: deprecated_parent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
+
+      expanded = described_class.expand_parent_tags([child])
+
+      expect(expanded).to include(
+        child,
+        deprecated_parent,
+        deprecated_grandparent,
+        active_ancestor
+      )
+      expect(expanded.reject(&:deprecated?)).to contain_exactly(child, active_ancestor)
+    end
+
+    it 'terminates when implications contain a cycle' do
+      first = create(:tag, name: 'expand_cycle_first')
+      second = create(:tag, name: 'expand_cycle_second')
+      TagImplication.create!(tag: first, parent_tag: second)
+      TagImplication.create!(tag: second, parent_tag: first)
+
+      expect(described_class.expand_parent_tags([first])).to contain_exactly(first, second)
+    end
+  end
+
+  describe 'deprecated validation' do
+    it 'rejects deprecated nico tags' do
+      tag = build(
+        :tag,
+        name: 'nico:deprecated_validation',
+        category: :nico,
+        deprecated_at: Time.current
+      )
+
+      expect(tag).not_to be_valid
+      expect(tag.errors[:deprecated_at]).to include('ニコタグは廃止できません．')
+    end
+  end
+
   describe '.merge_tags!' do
     let!(:target_tag) { create(:tag, category: :general) }
     let!(:source_tag) { create(:tag, category: :general) }
diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 2e6e432..18d5b73 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -736,16 +736,22 @@ RSpec.describe 'Posts API', type: :request do
       )
     end
 
-    it 'expands through deprecated parent tags and saves active ancestors' do
+    it 'expands through multiple deprecated parent tags and saves active ancestors' do
       child = Tag.create!(name: 'active_child', category: :general)
       deprecated_parent = Tag.create!(
         name: 'deprecated_parent',
         category: :general,
         deprecated_at: Time.current
       )
+      deprecated_grandparent = Tag.create!(
+        name: 'deprecated_grandparent',
+        category: :general,
+        deprecated_at: Time.current
+      )
       active_grandparent = Tag.create!(name: 'active_grandparent', category: :general)
       TagImplication.create!(tag: child, parent_tag: deprecated_parent)
-      TagImplication.create!(tag: deprecated_parent, parent_tag: active_grandparent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_grandparent)
       sign_in_as(member)
 
       post '/posts', params: post_write_params(
@@ -758,7 +764,7 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:created)
       saved_names = Post.find(json.fetch('id')).tags.map(&:name)
       expect(saved_names).to include('active_child', 'active_grandparent')
-      expect(saved_names).not_to include('deprecated_parent')
+      expect(saved_names).not_to include('deprecated_parent', 'deprecated_grandparent')
     end
 
     context "when nico tag already exists in tags" do
diff --git a/backend/spec/requests/tag_versions_spec.rb b/backend/spec/requests/tag_versions_spec.rb
index 8f092b3..62afeb8 100644
--- a/backend/spec/requests/tag_versions_spec.rb
+++ b/backend/spec/requests/tag_versions_spec.rb
@@ -21,6 +21,7 @@ RSpec.describe 'TagVersions API', type: :request do
     event_type:,
     name:,
     category:,
+    deprecated_at: nil,
     aliases: [],
     parent_tags: [],
     created_by_user:,
@@ -33,6 +34,7 @@ RSpec.describe 'TagVersions API', type: :request do
             event_type: event_type,
             name: name,
             category: category,
+            deprecated_at: deprecated_at,
             aliases: Array(aliases).join(' '),
             parent_tag_ids: Array(parent_tags).map(&:id).join(' '),
             created_by_user: created_by_user,
@@ -65,6 +67,7 @@ RSpec.describe 'TagVersions API', type: :request do
       event_type: 'update',
       name: 'new_tag_name',
       category: 'meme',
+      deprecated_at: t_v2,
       aliases: ['alias_shared', 'alias_new'],
       parent_tags: [parent_shared, parent_new],
       created_by_user: member,
@@ -133,6 +136,10 @@ RSpec.describe 'TagVersions API', type: :request do
         'current' => 'meme',
         'prev' => 'general'
       )
+      expect(latest.fetch('deprecated_at')).to eq(
+        'current' => t_v2.iso8601,
+        'prev' => nil
+      )
       expect(latest.fetch('aliases')).to include(
         { 'name' => 'alias_shared', 'type' => 'context' },
         { 'name' => 'alias_new', 'type' => 'added' },
@@ -178,6 +185,10 @@ RSpec.describe 'TagVersions API', type: :request do
         'current' => 'general',
         'prev' => nil
       )
+      expect(first.fetch('deprecated_at')).to eq(
+        'current' => nil,
+        'prev' => nil
+      )
       expect(first.fetch('aliases')).to include(
         { 'name' => 'alias_shared', 'type' => 'added' },
         { 'name' => 'alias_old', 'type' => 'added' }
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 26fe9c3..927b4a7 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -80,7 +80,7 @@ RSpec.describe 'Tags API', type: :request do
       deprecated_tag = Tag.create!(
         name: 'deprecated_filter',
         category: :general,
-        deprecated_at: Time.current
+        deprecated_at: 1.day.from_now
       )
       active_tag = Tag.create!(name: 'active_filter', category: :general)
 
@@ -473,6 +473,32 @@ RSpec.describe 'Tags API', type: :request do
         expect(versions.second.created_by_user_id).to eq(member_user.id)
       end
 
+      it 'updates deprecated state and records it in tag versions' do
+        expect {
+          patch "/tags/#{ tag.id }", params: { deprecated: '1' }
+        }.to change(TagVersion, :count).by(2)
+
+        expect(response).to have_http_status(:ok)
+        expect(tag.reload.deprecated_at).to be_present
+
+        versions = tag.tag_versions.order(:version_no)
+        expect(versions.first.deprecated_at).to be_nil
+        expect(versions.second.deprecated_at).to eq(tag.deprecated_at)
+        expect(json.fetch('deprecated_at')).to be_present
+      end
+
+      it 'rejects deprecating a nico tag' do
+        nico_tag = Tag.create!(name: 'nico:deprecated_update', category: :nico)
+
+        patch "/tags/#{ nico_tag.id }", params: { deprecated: '1' }
+
+        expect(response).to have_http_status(:unprocessable_entity)
+        expect(nico_tag.reload.deprecated_at).to be_nil
+        expect(json.fetch('errors')).to include(
+          'deprecated' => ['ニコタグは廃止できません．']
+        )
+      end
+
       it 'returns 422 when changing normal tag category to nico' do
         expect {
           patch "/tags/#{tag.id}", params: { category: 'nico' }
@@ -641,6 +667,91 @@ RSpec.describe 'Tags API', type: :request do
       expect(json.map { |item| item.fetch('name') }).to eq(['depth_visible_descendant'])
       expect(json.map { |item| item.fetch('name') }).not_to include('depth_deprecated_middle')
     end
+
+    it 'passes through multiple deprecated tags for roots and has_children' do
+      active_child = Tag.create!(
+        name: 'depth_active_child_below_deprecated',
+        category: :character
+      )
+      deprecated_parent = Tag.create!(
+        name: 'depth_deprecated_parent',
+        category: :character,
+        deprecated_at: Time.current
+      )
+      deprecated_grandparent = Tag.create!(
+        name: 'depth_deprecated_grandparent',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      active_ancestor = Tag.create!(
+        name: 'depth_active_ancestor',
+        category: :meme
+      )
+      TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
+      TagImplication.create!(tag: deprecated_parent, parent_tag: deprecated_grandparent)
+      TagImplication.create!(tag: deprecated_grandparent, parent_tag: active_ancestor)
+
+      get '/tags/with-depth'
+
+      root_names = json.map { |item| item.fetch('name') }
+      expect(root_names).to include('depth_active_ancestor')
+      expect(root_names).not_to include('depth_active_child_below_deprecated')
+      ancestor_json = json.find { |item| item.fetch('id') == active_ancestor.id }
+      expect(ancestor_json.fetch('has_children')).to eq(true)
+
+      get '/tags/with-depth', params: { parent: active_ancestor.id }
+
+      expect(json.map { |item| item.fetch('name') }).to include(
+        'depth_active_child_below_deprecated'
+      )
+      expect(json.map { |item| item.fetch('name') }).not_to include(
+        'depth_deprecated_parent',
+        'depth_deprecated_grandparent'
+      )
+    end
+
+    it 'treats an active tag with only deprecated ancestors as a root' do
+      active_child = Tag.create!(
+        name: 'depth_root_below_deprecated',
+        category: :character
+      )
+      deprecated_parent = Tag.create!(
+        name: 'depth_root_deprecated_parent',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      TagImplication.create!(tag: active_child, parent_tag: deprecated_parent)
+
+      get '/tags/with-depth'
+
+      expect(json.map { |item| item.fetch('name') }).to include(
+        'depth_root_below_deprecated'
+      )
+      expect(json.map { |item| item.fetch('name') }).not_to include(
+        'depth_root_deprecated_parent'
+      )
+    end
+
+    it 'terminates when deprecated implications contain a cycle' do
+      first = Tag.create!(
+        name: 'depth_cycle_first',
+        category: :character,
+        deprecated_at: Time.current
+      )
+      second = Tag.create!(
+        name: 'depth_cycle_second',
+        category: :material,
+        deprecated_at: Time.current
+      )
+      TagImplication.create!(tag: first, parent_tag: root_material)
+      TagImplication.create!(tag: second, parent_tag: first)
+      TagImplication.create!(tag: first, parent_tag: second)
+
+      get '/tags/with-depth', params: { parent: root_material.id }
+
+      expect(response).to have_http_status(:ok)
+      expect(json).to eq([])
+    end
   end
 
   describe 'GET /tags/name/:name/materials' do
diff --git a/backend/spec/requests/wiki_spec.rb b/backend/spec/requests/wiki_spec.rb
index 9b6e8c1..614180e 100644
--- a/backend/spec/requests/wiki_spec.rb
+++ b/backend/spec/requests/wiki_spec.rb
@@ -18,6 +18,13 @@ RSpec.describe 'Wiki API', type: :request do
         created_by_user: user,
         message: 'init')
   end
+  let!(:tag) do
+    Tag.create!(
+      tag_name: tn,
+      category: :general,
+      deprecated_at: Time.zone.local(2026, 6, 1)
+    )
+  end
 
   describe 'GET /wiki' do
     it 'returns wiki pages with title' do
@@ -30,6 +37,8 @@ RSpec.describe 'Wiki API', type: :request do
 
       expect(json[0]).to have_key('title')
       expect(json.map { |p| p['title'] }).to include('spec_wiki_title')
+      wiki_json = json.find { |item| item.fetch('id') == page.id }
+      expect(wiki_json.fetch('deprecated_at')).to eq(tag.deprecated_at.iso8601(3))
     end
   end
 
@@ -48,7 +57,8 @@ RSpec.describe 'Wiki API', type: :request do
 
         expect(json).to include(
             'id' => page.id,
-            'title' => 'spec_wiki_title')
+            'title' => 'spec_wiki_title',
+            'deprecated_at' => tag.deprecated_at.iso8601(3))
       end
     end
 
@@ -409,7 +419,11 @@ RSpec.describe 'Wiki API', type: :request do
         'kind' => 'content',
         'message' => 'r2'
       )
-      expect(top['wiki_page']).to include('id' => page.id, 'title' => 'spec_wiki_title')
+      expect(top['wiki_page']).to include(
+        'id' => page.id,
+        'title' => 'spec_wiki_title',
+        'deprecated_at' => tag.deprecated_at.iso8601(3)
+      )
       expect(top['user']).to include('id' => user.id, 'name' => user.name)
       expect(top).to have_key('timestamp')
 
@@ -479,6 +493,7 @@ RSpec.describe 'Wiki API', type: :request do
       expect(json).to include(
         'wiki_page_id' => page.id,
         'title' => 'spec_wiki_title',
+        'deprecated_at' => tag.deprecated_at.iso8601(3),
         'older_revision_id' => rev_a.id,
         'newer_revision_id' => rev_b.id
       )
diff --git a/frontend/src/pages/wiki/WikiDetailPage.test.tsx b/frontend/src/pages/wiki/WikiDetailPage.test.tsx
new file mode 100644
index 0000000..4b7b8c7
--- /dev/null
+++ b/frontend/src/pages/wiki/WikiDetailPage.test.tsx
@@ -0,0 +1,54 @@
+import { screen } from '@testing-library/react'
+import { Route, Routes } from 'react-router-dom'
+import { describe, expect, it, vi } from 'vitest'
+
+import WikiDetailPage from '@/pages/wiki/WikiDetailPage'
+import { buildTag, buildWikiPage } from '@/test/factories'
+import { renderWithProviders } from '@/test/render'
+
+const wikiApi = vi.hoisted (() => ({
+  fetchWikiPage:        vi.fn (),
+  fetchWikiPageByTitle: vi.fn (),
+}))
+
+const tagsApi = vi.hoisted (() => ({
+  fetchTagByName: vi.fn (),
+}))
+
+const postsApi = vi.hoisted (() => ({
+  fetchPosts: vi.fn (),
+}))
+
+vi.mock ('@/lib/wiki', () => wikiApi)
+vi.mock ('@/lib/tags', () => tagsApi)
+vi.mock ('@/lib/posts', () => postsApi)
+
+describe ('WikiDetailPage', () => {
+  it ('renders deprecated state outside the wiki title link', async () => {
+    wikiApi.fetchWikiPageByTitle.mockResolvedValueOnce (buildWikiPage ({
+      title:        '旧タグ',
+      deprecatedAt: '2026-06-01T00:00:00.000Z',
+    }))
+    tagsApi.fetchTagByName.mockResolvedValueOnce (buildTag ({
+      name:         '旧タグ',
+      deprecatedAt: '2026-06-01T00:00:00.000Z',
+    }))
+    postsApi.fetchPosts.mockResolvedValueOnce ({ posts: [], count: 0 })
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/wiki/:title" element={<WikiDetailPage/>}/>
+        </Routes>,
+        { route: '/wiki/%E6%97%A7%E3%82%BF%E3%82%B0' },
+    )
+
+    const marker = await screen.findByText ('（廃止）')
+    const heading = marker.closest ('h1')
+    const link = screen.getByRole ('link', { name: '旧タグ' })
+
+    expect (heading).not.toBeNull ()
+    expect (heading!).toHaveTextContent ('旧タグ（廃止）')
+    expect (link).toBeInTheDocument ()
+    expect (marker.closest ('a')).toBeNull ()
+  })
+})
diff --git a/frontend/src/pages/wiki/WikiDiffPage.test.tsx b/frontend/src/pages/wiki/WikiDiffPage.test.tsx
index 24d71eb..185b904 100644
--- a/frontend/src/pages/wiki/WikiDiffPage.test.tsx
+++ b/frontend/src/pages/wiki/WikiDiffPage.test.tsx
@@ -16,6 +16,7 @@ describe ('WikiDiffPage', () => {
     api.apiGet.mockResolvedValueOnce ({
       wikiPageId:      3,
       title:           '差分対象',
+      deprecatedAt:    null,
       olderRevisionId: 1,
       newerRevisionId: 2,
       diff: [
@@ -43,4 +44,26 @@ describe ('WikiDiffPage', () => {
     expect (screen.getByText ('added line')).toBeInTheDocument ()
     expect (screen.getByText ('removed line')).toBeInTheDocument ()
   })
+
+  it ('appends deprecated state to the wiki title', async () => {
+    api.apiGet.mockResolvedValueOnce ({
+      wikiPageId:      3,
+      title:           '廃止 Wiki',
+      deprecatedAt:    '2026-06-01T00:00:00.000Z',
+      olderRevisionId: 1,
+      newerRevisionId: 2,
+      diff:            [],
+    })
+
+    renderWithProviders (
+        <Routes>
+          <Route path="/wiki/:id/diff" element={<WikiDiffPage/>}/>
+        </Routes>,
+        { route: '/wiki/3/diff?from=1&to=2' },
+    )
+
+    expect (await screen.findByRole ('heading', {
+      name: '廃止 Wiki（廃止）',
+    })).toBeInTheDocument ()
+  })
 })
diff --git a/frontend/src/pages/wiki/WikiHistoryPage.test.tsx b/frontend/src/pages/wiki/WikiHistoryPage.test.tsx
new file mode 100644
index 0000000..35aa8f5
--- /dev/null
+++ b/frontend/src/pages/wiki/WikiHistoryPage.test.tsx
@@ -0,0 +1,38 @@
+import { screen } from '@testing-library/react'
+import { describe, expect, it, vi } from 'vitest'
+
+import WikiHistoryPage from '@/pages/wiki/WikiHistoryPage'
+import { renderWithProviders } from '@/test/render'
+
+const api = vi.hoisted (() => ({
+  apiGet: vi.fn (),
+}))
+
+vi.mock ('@/lib/api', () => api)
+
+describe ('WikiHistoryPage', () => {
+  it ('renders deprecated state outside the wiki title link', async () => {
+    api.apiGet.mockResolvedValueOnce ([{
+      revisionId:  2,
+      pred:        1,
+      succ:        null,
+      wikiPage:    {
+	id:           3,
+	title:        '旧タグ',
+	deprecatedAt: '2026-06-01T00:00:00.000Z',
+      },
+      user:        { id: 4, name: 'tester' },
+      kind:        'content',
+      message:     'updated',
+      timestamp:   '2026-06-02T00:00:00.000Z',
+    }])
+
+    renderWithProviders (<WikiHistoryPage/>)
+
+    const link = await screen.findByRole ('link', { name: '旧タグ' })
+    const marker = screen.getByText ('（廃止）')
+
+    expect (link).toHaveAttribute ('href', '/wiki/%E6%97%A7%E3%82%BF%E3%82%B0?version=2')
+    expect (marker.closest ('a')).toBeNull ()
+  })
+})
diff --git a/frontend/src/pages/wiki/WikiSearchPage.test.tsx b/frontend/src/pages/wiki/WikiSearchPage.test.tsx
index fd87e1b..e831035 100644
--- a/frontend/src/pages/wiki/WikiSearchPage.test.tsx
+++ b/frontend/src/pages/wiki/WikiSearchPage.test.tsx
@@ -53,6 +53,10 @@ describe ('WikiSearchPage', () => {
 
     renderWithProviders (<WikiSearchPage/>)
 
-    expect (await screen.findByRole ('link', { name: '旧タグ（廃止）' })).toBeInTheDocument ()
+    const link = await screen.findByRole ('link', { name: '旧タグ' })
+    const marker = screen.getByText ('（廃止）')
+
+    expect (link).toBeInTheDocument ()
+    expect (marker.closest ('a')).toBeNull ()
   })
 })