diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index e8cae00..96f520c 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -95,9 +95,10 @@ class PostsController < ApplicationController
   end
 
   def random
-    post = filtered_posts.preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
-                         .order('RAND()')
-                         .first
+    post = filtered_posts
+           .preload(tags: [:deerjikists, :materials, { tag_name: :wiki_page }])
+           .order('RAND()')
+           .first
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
@@ -108,7 +109,7 @@ class PostsController < ApplicationController
     return head :not_found unless post
 
     render json: PostRepr.base(post, current_user)
-                         .merge(tags: build_tag_tree_for(post.tags),
+                         .merge(tags: build_tag_tree_for(post),
                                 related: PostRepr.many(post.related(limit: 20)))
   end
 
@@ -132,11 +133,11 @@ class PostsController < ApplicationController
     ApplicationRecord.transaction do
       post.save!
 
-      tags = Tag.normalise_tags!(tag_names)
+      Tag.normalise_tags!(tag_names, with_sections: true) => { tags:, sections: }
       TagVersioning.record_tag_snapshots!(tags, created_by_user: current_user)
 
       tags = Tag.expand_parent_tags(tags)
-      sync_post_tags!(post, tags)
+      sync_post_tags!(post, tags, sections)
 
       sync_parent_posts!(post, parent_post_ids)
 
@@ -235,7 +236,7 @@ class PostsController < ApplicationController
 
     post.reload
     json = PostRepr.base(post, current_user)
-    json['tags'] = build_tag_tree_for(post.tags)
+    json['tags'] = build_tag_tree_for(post)
     render json:, status: :ok
   rescue Tag::NicoTagNormalisationError
     head :bad_request
@@ -337,7 +338,7 @@ class PostsController < ApplicationController
   def tagged_post_ids_for(name) =
       Post.joins(tags: :tag_name).where(tag_names: { name: }).select(:id)
 
-  def sync_post_tags! post, desired_tags
+  def sync_post_tags! post, desired_tags, sections
     desired_tags.each do |t|
       t.save! if t.new_record?
     end
@@ -356,13 +357,20 @@ class PostsController < ApplicationController
       end
     end
 
+    PostTagSection.where(post_id: post.id).destroy_all
+    sections.each do |tag_id, ranges|
+      ranges.each do |begin_ms, end_ms|
+        PostTagSection.create!(post_id: post.id, tag_id:, begin_ms:, end_ms:)
+      end
+    end
+
     PostTag.where(post_id: post.id, tag_id: to_remove.to_a).kept.find_each do |pt|
       pt.discard_by!(current_user)
     end
   end
 
-  def build_tag_tree_for tags
-    tags = tags.to_a
+  def build_tag_tree_for post
+    tags = post.tags.to_a
     tag_ids = tags.map(&:id)
 
     implications = TagImplication.where(parent_tag_id: tag_ids, tag_id: tag_ids)
@@ -384,8 +392,11 @@ class PostsController < ApplicationController
       tag = tags_by_id[tag_id]
       return nil unless tag
 
+      sections = PostTagSection.where(post_id: post.id, tag_id: tag.id)
+                 .as_json(only: [:begin_ms, :end_ms])
+
       if path.include?(tag_id)
-        return TagRepr.base(tag).merge(children: [])
+        return TagRepr.base(tag).merge(children: [], sections:)
       end
 
       if memo.key?(tag_id)
@@ -397,7 +408,7 @@ class PostsController < ApplicationController
 
       children = child_ids.filter_map { |cid| build_node.(cid, new_path) }
 
-      memo[tag_id] = TagRepr.base(tag).merge(children:)
+      memo[tag_id] = TagRepr.base(tag).merge(children:, sections:)
     end
 
     root_ids.filter_map { |id| build_node.call(id, []) }
@@ -470,7 +481,21 @@ class PostsController < ApplicationController
   end
 
   def editable_tag_names_from_post post
-    post.tags.not_nico.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+    post
+        .post_tags
+        .kept
+        .joins(tag: :tag_name)
+        .merge(Tag.not_nico)
+        .includes(:sections, tag: :tag_name)
+        .order('tag_names.name')
+        .map do |post_tag|
+      name = post_tag.tag.tag_name.name
+      sections = post_tag.sections.sort_by(&:begin_ms)
+
+      next name if sections.empty?
+
+      "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
+    end
   end
 
   def post_incoming_snapshot title:, original_created_from:, original_created_before:,
@@ -502,9 +527,16 @@ class PostsController < ApplicationController
   end
 
   def incoming_tag_names_for_snapshot raw_tag_names
-    tags = Tag.normalise_tags!(raw_tag_names, with_tagme: false)
+    Tag.normalise_tags!(raw_tag_names, with_tagme: false, with_sections: true) =>
+        { tags:, sections: }
+
+    Tag.expand_parent_tags(tags).uniq(&:id).map { |tag|
+      "#{ tag.name }#{ sections[tag.id].to_a.map { section_literal(_1) }.join }"
+    }.sort
+  end
 
-    Tag.expand_parent_tags(tags).map(&:name).uniq.sort
+  def section_literal section
+    "[#{ Post.ms_to_time(section[0]) }-#{ Post.ms_to_time(section[1]) }]"
   end
 
   def post_conflict_json post:, base_version_no:, base_snapshot:,
@@ -591,7 +623,8 @@ class PostsController < ApplicationController
                  original_created_from: snapshot[:original_created_from],
                  original_created_before: snapshot[:original_created_before])
 
-    editable_tags = Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false)
+    Tag.normalise_tags!(snapshot[:tag_names], with_tagme: false, with_sections: true) =>
+        { tags: editable_tags, sections: }
     TagVersioning.record_tag_snapshots!(editable_tags, created_by_user: current_user)
 
     readonly_tags = post.tags.nico.to_a
@@ -599,7 +632,7 @@ class PostsController < ApplicationController
     tags = readonly_tags + editable_tags
     tags = Tag.expand_parent_tags(tags)
 
-    sync_post_tags!(post, tags)
+    sync_post_tags!(post, tags, sections)
     sync_parent_posts!(post, snapshot[:parent_post_ids])
 
     PostVersionRecorder.record!(post:, event_type: :update, created_by_user: current_user)
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 4c3ddb1..8970119 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -56,7 +56,38 @@ class Post < ApplicationRecord
     super(options).merge(thumbnail: nil)
   end
 
-  def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
+  def snapshot_tag_names
+    post_tags
+        .kept
+        .joins(tag: :tag_name)
+        .includes(:sections, tag: :tag_name)
+        .order('tag_names.name')
+        .map do |post_tag|
+      name = post_tag.tag.tag_name.name
+      sections = post_tag.sections.sort_by(&:begin_ms)
+
+      next name if sections.empty?
+
+      "#{ name }#{ sections.map { Post.section_literal(_1) }.join }"
+    end
+  end
+
+  def self.section_literal section
+    "[#{ Post.ms_to_time(section.begin_ms) }-#{ Post.ms_to_time(section.end_ms) }]"
+  end
+
+  def self.ms_to_time ms
+    total_s = ms / 1_000
+    s = total_s % 60
+    min = (total_s / 60) % 60
+    h = total_s / 3_600
+
+    if h.positive?
+      '%d:%02d:%02d' % [h, min, s]
+    else
+      '%d:%02d' % [min, s]
+    end
+  end
 
   def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
 
diff --git a/backend/app/models/post_tag.rb b/backend/app/models/post_tag.rb
index 702f66a..ac56c77 100644
--- a/backend/app/models/post_tag.rb
+++ b/backend/app/models/post_tag.rb
@@ -10,6 +10,12 @@ class PostTag < ApplicationRecord
   belongs_to :created_user, class_name: 'User', optional: true
   belongs_to :deleted_user, class_name: 'User', optional: true
 
+  has_many :sections, -> { order(:begin_ms) }, class_name: 'PostTagSection',
+                                               foreign_key: [:post_id, :tag_id],
+                                               primary_key: [:post_id, :tag_id],
+                                               dependent: :delete_all,
+                                               inverse_of: :post_tag
+
   validates :post_id, presence: true
   validates :tag_id, presence: true
   validates :post_id, uniqueness: {
diff --git a/backend/app/models/post_tag_section.rb b/backend/app/models/post_tag_section.rb
new file mode 100644
index 0000000..8d6af9e
--- /dev/null
+++ b/backend/app/models/post_tag_section.rb
@@ -0,0 +1,20 @@
+class PostTagSection < ApplicationRecord
+  self.primary_key = :post_id, :tag_id, :begin_ms
+
+  belongs_to :post
+  belongs_to :tag
+
+  belongs_to :post_tag, -> { kept }, foreign_key: [:post_id, :tag_id],
+                                     primary_key: [:post_id, :tag_id],
+                                     inverse_of: :sections,
+                                     optional: true
+
+  validates :post_id, presence: true
+  validates :tag_id, presence: true
+
+  validates :begin_ms, presence: true,
+                       numericality: { only_integer: true, greater_than_or_equal_to: 0 }
+
+  validates :end_ms, presence: true,
+                     numericality: { only_integer: true, greater_than: :begin_ms }
+end
diff --git a/backend/app/models/tag.rb b/backend/app/models/tag.rb
index 51ca783..0015250 100644
--- a/backend/app/models/tag.rb
+++ b/backend/app/models/tag.rb
@@ -92,22 +92,45 @@ class Tag < ApplicationRecord
 
   def self.normalise_tags! tag_names, with_tagme: true,
                                       with_no_deerjikist: true,
-                                      deny_nico: true
+                                      deny_nico: true,
+                                      with_sections: false
     if deny_nico && tag_names.any? { |n| n.downcase.start_with?('nico:') }
       raise NicoTagNormalisationError
     end
 
+    sections = { }
     tags = tag_names.map do |name|
       pf, cat = CATEGORY_PREFIXES.find { |p, _| name.downcase.start_with?(p) } || ['', nil]
+
       name = TagName.canonicalise(name.sub(/\A#{ pf }/i, '')).first
+
+      sections_by_tag = []
+      while n = name.sub!(/^(\S*?)\[([0-9:.]*?)-([0-9:.]*?)\](\S*?)$/, '\1\4 \2 \3')
+        name, *section_raw = n.split
+
+        begin_ms, end_ms = section_raw.map { time_to_ms(_1) }
+        next if begin_ms == end_ms
+
+        begin_ms, end_ms = end_ms, begin_ms if begin_ms > end_ms
+
+        sections_by_tag << [begin_ms, end_ms]
+      end
+
       find_or_create_by_tag_name!(name, category: (cat || :general)).tap do |tag|
         tag.update!(category: cat) if cat && tag.category != cat
+        sections[tag.id] = sections_by_tag if sections_by_tag.present?
       end
     end
 
     tags << Tag.tagme if with_tagme && tags.size < 10 && tags.none?(Tag.tagme)
     tags << Tag.no_deerjikist if with_no_deerjikist && tags.all? { |t| !(t.deerjikist?) }
-    tags.uniq(&:id)
+    tags.uniq!(&:id)
+
+    if with_sections
+      { tags:, sections: }
+    else
+      tags
+    end
   end
 
   def self.expand_parent_tags tags
@@ -228,4 +251,23 @@ class Tag < ApplicationRecord
       errors.add :category, 'ニジラーと紐づいてゐるタグはニジラー・カテゴリである必要があります．'
     end
   end
+
+  def self.time_to_ms str
+    parts = str.split(':')
+
+    s_part = parts.pop
+    s, ms = s_part.split('.')
+
+    total_s = s.to_i
+
+    if parts.length >= 1
+      total_s += parts.pop.to_i * 60
+    end
+
+    if parts.length >= 1
+      total_s += parts.pop.to_i * 3_600
+    end
+
+    total_s * 1_000 + ms.to_s.ljust(3, '0')[0, 3].to_i
+  end
 end
diff --git a/backend/db/migrate/20260518235300_create_post_tag_sections.rb b/backend/db/migrate/20260518235300_create_post_tag_sections.rb
new file mode 100644
index 0000000..ff87e20
--- /dev/null
+++ b/backend/db/migrate/20260518235300_create_post_tag_sections.rb
@@ -0,0 +1,19 @@
+class CreatePostTagSections < ActiveRecord::Migration[8.0]
+  def change
+    create_table :post_tag_sections, primary_key: [:post_id, :tag_id, :begin_ms] do |t|
+      t.references :post, null: false, foreign_key: true, index: false
+      t.references :tag, null: false, foreign_key: true, index: false
+      t.integer :begin_ms, null: false
+      t.integer :end_ms, null: false
+      t.timestamps
+
+      t.index [:post_id, :begin_ms], name: 'idx_post_tag_sections_post_id_begin_ms'
+
+      t.check_constraint 'begin_ms >= 0',
+                         name: 'chk_post_tag_sections_begin_ms_natural'
+
+      t.check_constraint 'begin_ms < end_ms',
+                         name: 'chk_post_tag_sections_end_ms_after_begin_ms'
+    end
+  end
+end
diff --git a/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb b/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb
new file mode 100644
index 0000000..8225e13
--- /dev/null
+++ b/backend/db/migrate/20260519013100_add_video_ms_to_posts.rb
@@ -0,0 +1,9 @@
+class AddVideoMsToPosts < ActiveRecord::Migration[8.0]
+  def change
+    add_column :posts, :video_ms, :integer
+    add_index :posts, [:video_ms, :id], name: 'idx_posts_video_ms_id'
+
+    add_check_constraint :posts, 'video_ms IS NULL OR video_ms > 0',
+                         name: 'chk_posts_video_ms_positive'
+  end
+end
diff --git a/backend/db/schema.rb b/backend/db/schema.rb
index 94edb82..60e80eb 100644
--- a/backend/db/schema.rb
+++ b/backend/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
+ActiveRecord::Schema[8.0].define(version: 2026_05_19_013100) do
   create_table "active_storage_attachments", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.string "name", null: false
     t.string "record_type", null: false
@@ -137,6 +137,19 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.index ["target_post_id"], name: "index_post_similarities_on_target_post_id"
   end
 
+  create_table "post_tag_sections", primary_key: ["post_id", "tag_id", "begin_ms"], charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
+    t.bigint "post_id", null: false
+    t.bigint "tag_id", null: false
+    t.integer "begin_ms", null: false
+    t.integer "end_ms", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["post_id", "begin_ms"], name: "idx_post_tag_sections_post_id_begin_ms"
+    t.index ["tag_id"], name: "fk_rails_8be3847903"
+    t.check_constraint "`begin_ms` < `end_ms`", name: "chk_post_tag_sections_end_ms_after_begin_ms"
+    t.check_constraint "`begin_ms` >= 0", name: "chk_post_tag_sections_begin_ms_natural"
+  end
+
   create_table "post_tags", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
     t.bigint "post_id", null: false
     t.bigint "tag_id", null: false
@@ -187,8 +200,11 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.datetime "original_created_before"
     t.datetime "updated_at", null: false
     t.integer "version_no", null: false
+    t.integer "video_ms"
     t.index ["uploaded_user_id"], name: "index_posts_on_uploaded_user_id"
     t.index ["url"], name: "index_posts_on_url", unique: true
+    t.index ["video_ms", "id"], name: "idx_posts_video_ms_id"
+    t.check_constraint "(`video_ms` is null) or (`video_ms` > 0)", name: "chk_posts_video_ms_positive"
     t.check_constraint "`version_no` > 0", name: "chk_posts_version_no_positive"
   end
 
@@ -290,6 +306,7 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.index ["expires_at"], name: "index_theatre_watching_users_on_expires_at"
+    t.index ["theatre_id", "expires_at"], name: "idx_on_theatre_id_skip_expires_at_4c8de1dd42"
     t.index ["theatre_id", "expires_at"], name: "index_theatre_watching_users_on_theatre_id_and_expires_at"
     t.index ["theatre_id"], name: "index_theatre_watching_users_on_theatre_id"
     t.index ["user_id"], name: "index_theatre_watching_users_on_user_id"
@@ -446,6 +463,8 @@ ActiveRecord::Schema[8.0].define(version: 2026_05_07_213300) do
   add_foreign_key "post_implications", "posts", column: "parent_post_id"
   add_foreign_key "post_similarities", "posts"
   add_foreign_key "post_similarities", "posts", column: "target_post_id"
+  add_foreign_key "post_tag_sections", "posts"
+  add_foreign_key "post_tag_sections", "tags"
   add_foreign_key "post_tags", "posts"
   add_foreign_key "post_tags", "tags"
   add_foreign_key "post_tags", "users", column: "created_user_id"
diff --git a/backend/spec/models/post_tag_spec.rb b/backend/spec/models/post_tag_spec.rb
new file mode 100644
index 0000000..551f3fd
--- /dev/null
+++ b/backend/spec/models/post_tag_spec.rb
@@ -0,0 +1,29 @@
+RSpec.describe PostTag, type: :model do
+  describe '#sections' do
+    it 'loads sections by post_id and tag_id' do
+      post_tag = create(:post_tag)
+      section = create(:post_tag_section,
+                       post: post_tag.post,
+                       tag: post_tag.tag,
+                       begin_ms: 1000,
+                       end_ms: 2000)
+
+      expect(post_tag.sections).to contain_exactly(section)
+    end
+
+    it 'does not load sections for another tag on the same post' do
+      post = create(:post)
+      tag = create(:tag)
+      other_tag = create(:tag)
+
+      post_tag = create(:post_tag, post:, tag:)
+      create(:post_tag_section,
+             post:,
+             tag: other_tag,
+             begin_ms: 1000,
+             end_ms: 2000)
+
+      expect(post_tag.sections).to be_empty
+    end
+  end
+end
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index bc1048e..4655f01 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -8,6 +8,7 @@ import { Button } from '@/components/ui/button'
 import { toast } from '@/components/ui/use-toast'
 import { isApiError } from '@/lib/api'
 import { updatePost } from '@/lib/posts'
+import { msToTime } from '@/lib/utils'
 
 import type { FC, FormEvent } from 'react'
 
@@ -25,7 +26,7 @@ const tagsToStr = (tags: Tag[]): string => {
 
   tags.filter (t => t.category !== 'nico').forEach (walk)
 
-  return [...(new Set (result.map (t => t.name)))].join (' ')
+  return [...(new Set (result.map (t => `${ t.name }${ t.sections.map (s => `[${ msToTime (s.beginMs) }-${ msToTime (s.endMs) }]`).join ('') }`)))].join (' ')
 }
 
 
@@ -167,4 +168,4 @@ const PostEditForm: FC<Props> = ({ post, onSave }) => {
       </form>)
 }
 
-export default PostEditForm
\ No newline at end of file
+export default PostEditForm
diff --git a/frontend/src/lib/utils.ts b/frontend/src/lib/utils.ts
index aac3785..672ebd2 100644
--- a/frontend/src/lib/utils.ts
+++ b/frontend/src/lib/utils.ts
@@ -71,3 +71,15 @@ export const originalCreatedAtString = (
 	       .join (' '))
   return rtn === '〜' ? '年月日不詳' : rtn
 }
+
+
+export const msToTime = (ms: number): string => {
+  const totalS = Math.trunc (ms / 1_000)
+  const s = String (totalS % 60)
+  const min = String (Math.trunc (totalS / 60) % 60)
+  const h = String (Math.trunc (totalS / 3_600))
+
+  return (h > 0
+	  ? `${ h }:${ min.padStart (2, '0') }:${ s.padStart (2, '0') }`
+	  : `${ min }:${ s.padStart (2, '0') }`)
+}
diff --git a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
index 69444b1..4901116 100644
--- a/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
+++ b/frontend/src/pages/deerjikists/DeerjikistDetailPage.tsx
@@ -1,5 +1,6 @@
 import { useQuery, useQueryClient } from '@tanstack/react-query'
 import { useEffect, useMemo, useState } from 'react'
+import { Helmet } from 'react-helmet-async'
 import { useParams } from 'react-router-dom'
 
 import TagLink from '@/components/TagLink'
@@ -69,6 +70,11 @@ const DeerjikistDetailPage: FC = () => {
 
   return (
       <MainArea>
+	<Helmet>
+	  <meta name="robots" content="noindex"/>
+	  {tag && <title>{tag.name} | ニジラー情報</title>}
+	</Helmet>
+
 	{(loading || !(tag)) ? 'Loading...' : (
 	    <div className="max-w-xl">
 	      <PageTitle>
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index e552f69..a4a7950 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -126,7 +126,7 @@ export type Post = {
     title:                  string | null
     thumbnail:              string | null
     thumbnailBase:          string | null
-    tags:                   Tag[]
+    tags:                   TagWithSections[]
     parentPosts?:           Post[]
     childPosts?:            Post[]
     siblingPosts?:          Record<`${ number }`, Post[]>
@@ -187,7 +187,6 @@ export type Tag = {
     hasWiki:        boolean
     materialId:     number | null
     hasDeerjikists: boolean
-    children?:      Tag[]
     matchedAlias?:  string | null }
 
 export type TagVersion = {
@@ -201,6 +200,10 @@ export type TagVersion = {
     createdAt:              string
     createdByUser:          { id: number; name: string | null } | null }
 
+export type TagWithSections = Tag & { sections: { beginMs:  number
+						  endMs:    number }[]
+			              children: TagWithSections[] }
+
 export type Theatre = {
     id:             number
     name:           string | null