diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index cfb0cbd..310c449 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -109,7 +109,7 @@ class PostsController < ApplicationController
 
     render json: PostRepr.base(post, current_user)
                          .merge(tags: build_tag_tree_for(post.tags),
-                                related: post.related(limit: 20))
+                                related: PostRepr.many(post.related(limit: 20)))
   end
 
   def create
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 63c23d2..02b4c08 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -37,18 +37,26 @@ class Post < ApplicationRecord
 
   def parent_posts = parents
 
+  def child_posts = children
+
+  def sibling_posts
+    parent_post_ids = parent_posts.order(:id).pluck(:id)
+
+    parent_post_ids.to_h { [_1, PostImplication.where(parent_post: _1).map(&:post)] }
+  end
+
   def as_json options = { }
-    super(options).merge({ thumbnail: thumbnail.attached? ?
-                                      Rails.application.routes.url_helpers.rails_blob_url(
-                                          thumbnail, only_path: false) :
-                                      nil })
+    super(options).merge(thumbnail: thumbnail.attached? ?
+                                    Rails.application.routes.url_helpers.rails_blob_url(
+                                        thumbnail, only_path: false) :
+                                    nil)
   rescue
     super(options).merge(thumbnail: nil)
   end
 
   def snapshot_tag_names = tags.joins(:tag_name).order('tag_names.name').pluck('tag_names.name')
 
-  def snapshot_parent_post_ids = parents.order(:parent_post_id).pulck(:parent_post_id)
+  def snapshot_parent_post_ids = parents.order(:parent_post_id).pluck(:parent_post_id)
 
   def related limit: nil
     ids = post_similarities.order(cos: :desc)
diff --git a/backend/app/representations/post_repr.rb b/backend/app/representations/post_repr.rb
index b77d0b8..87f59f9 100644
--- a/backend/app/representations/post_repr.rb
+++ b/backend/app/representations/post_repr.rb
@@ -3,7 +3,7 @@
 
 module PostRepr
   BASE = { include: { tags: TagRepr::BASE, uploaded_user: UserRepr::BASE },
-           methods: [:parent_posts] }.freeze
+           methods: [:parent_posts, :child_posts, :sibling_posts] }.freeze
 
   module_function
 
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 8c3411b..5558e69 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -4,6 +4,7 @@ import PostFormTagsArea from '@/components/PostFormTagsArea'
 import PostOriginalCreatedTimeField from '@/components/PostOriginalCreatedTimeField'
 import Label from '@/components/common/Label'
 import { Button } from '@/components/ui/button'
+import { toast } from '@/components/ui/use-toast'
 import { apiPut } from '@/lib/api'
 
 import type { FC } from 'react'
@@ -35,20 +36,30 @@ export default (({ post, onSave }: Props) => {
       useState<string | null> (post.originalCreatedBefore)
   const [originalCreatedFrom, setOriginalCreatedFrom] =
       useState<string | null> (post.originalCreatedFrom)
-  const [title, setTitle] = useState (post.title)
+  const [parentPostIds, setParentPostIds] = useState (post.parentPosts!.map (p => p.id).join (' '))
   const [tags, setTags] = useState<string> ('')
+  const [title, setTitle] = useState (post.title)
 
   const handleSubmit = async () => {
-    const data = await apiPut<Post> (
-	`/posts/${ post.id }`,
-	{ title, tags, original_created_from: originalCreatedFrom,
-	  original_created_before: originalCreatedBefore },
-	{ headers: { 'Content-Type': 'multipart/form-data' } })
-    onSave ({ ...post,
-	      title:                  data.title,
-	      tags:                   data.tags,
-	      originalCreatedFrom:    data.originalCreatedFrom,
-	      originalCreatedBefore:  data.originalCreatedBefore } as Post)
+    try
+    {
+      const data = await apiPut<Post> (
+	  `/posts/${ post.id }`,
+	  { title, tags, parent_post_ids: parentPostIds,
+	    original_created_from: originalCreatedFrom,
+	    original_created_before: originalCreatedBefore },
+	  { headers: { 'Content-Type': 'multipart/form-data' } })
+      onSave ({ ...post,
+		title:                  data.title,
+		tags:                   data.tags,
+		originalCreatedFrom:    data.originalCreatedFrom,
+		originalCreatedBefore:  data.originalCreatedBefore } as Post)
+      toast ({ description: '更新しました．' })
+    }
+    catch
+    {
+      toast ({ description: '更新はできなかったよ……' })
+    }
   }
 
   useEffect (() => {
@@ -66,6 +77,16 @@ export default (({ post, onSave }: Props) => {
 		 onChange={ev => setTitle (ev.target.value)}/>
 	</div>
 
+	{/* 親投稿 */}
+	<div>
+	  <Label>親投稿</Label>
+	  <input
+	      type="text"
+	      value={parentPostIds}
+	      onChange={e => setParentPostIds (e.target.value)}
+	      className="w-full border p-2 rounded"/>
+	</div>
+
 	{/* タグ */}
 	<PostFormTagsArea tags={tags} setTags={setTags}/>
 
diff --git a/frontend/src/components/PostList.tsx b/frontend/src/components/PostList.tsx
index c072154..582762e 100644
--- a/frontend/src/components/PostList.tsx
+++ b/frontend/src/components/PostList.tsx
@@ -3,6 +3,7 @@ import { useRef } from 'react'
 import { useLocation } from 'react-router-dom'
 
 import PrefetchLink from '@/components/PrefetchLink'
+import { cn } from '@/lib/utils'
 import { useSharedTransitionStore } from '@/stores/sharedTransitionStore'
 
 import type { FC, MouseEvent } from 'react'
@@ -39,8 +40,10 @@ export default (({ posts, onClick }: Props) => {
 		<motion.div
 		    ref={cardRef}
 		    layoutId={layoutId}
-		    className="w-full h-full overflow-hidden rounded-xl shadow
-			       transform-gpu will-change-transform"
+		    className={cn ('w-full h-full overflow-hidden rounded-xl shadow',
+				   'transform-gpu will-change-transform',
+				   (post.childPosts ?? []).length > 0 && 'border-4 border-green-500',
+				   (post.parentPosts ?? []).length > 0 && 'border-4 border-yellow-500')}
 		    whileHover={{ scale: 1.02 }}
 		    onLayoutAnimationStart={() => {
 		      if (!(cardRef.current))
diff --git a/frontend/src/pages/posts/PostDetailPage.tsx b/frontend/src/pages/posts/PostDetailPage.tsx
index 433d312..5cefce7 100644
--- a/frontend/src/pages/posts/PostDetailPage.tsx
+++ b/frontend/src/pages/posts/PostDetailPage.tsx
@@ -21,7 +21,7 @@ import ServiceUnavailable from '@/pages/ServiceUnavailable'
 
 import type { FC } from 'react'
 
-import type { NiconicoViewerHandle, User } from '@/types'
+import type { NiconicoViewerHandle, Post, User } from '@/types'
 
 type Props = { user: User | null }
 
@@ -108,7 +108,34 @@ export default (({ user }: Props) => {
 	  {post
 	   ? (
 	      <>
-		{/* TODO: 親投稿リスト */}
+		{(post.childPosts ?? []).length > 0 && (
+		    <div className="mb-4 bg-green-200 dark:bg-green-800 text-sm p-2 rounded-md">
+		      <p>この投稿には {post.childPosts!.length} 件の子投稿があります．</p>
+		      <PostList posts={[{ ...post, childPosts: [{ } as Post] },
+					...post.childPosts!.map (p => ({
+					    ...p, parentPosts: [{ } as Post] }))]}/>
+		    </div>
+		)}
+		{(post.parentPosts ?? []).map (pp => {
+		  const siblings = post.siblingPosts?.[String (pp.id) as `${ number }`]
+		  if (!(siblings))
+		    return
+
+		  return (
+		      <div
+			  key={pp.id}
+			  className="mb-4 bg-yellow-200 dark:bg-yellow-800 text-sm p-2 rounded-md">
+			<p>
+			  この投稿には 1 件の親投稿{
+			      siblings.length > 1
+			      && `と ${ siblings.length - 1 } 件の姉妹投稿`}があります．
+			</p>
+			<PostList posts={[{ ...pp, childPosts: [{ } as Post] },
+					  ...siblings.map (p => ({
+					      ...p, parentPosts: [{ } as Post] }))]}/>
+		      </div>)
+		})}
+
 		{(post.thumbnail || post.thumbnailBase) && (
 		    <motion.div
 			layoutId={`page-${ id }`}
@@ -147,7 +174,6 @@ export default (({ user }: Props) => {
 					       (prev: any) => newPost ?? prev)
 			      qc.invalidateQueries ({ queryKey: postsKeys.root })
 			      qc.invalidateQueries ({ queryKey: tagsKeys.root })
-			      toast ({ description: '更新しました．' })
 			    }}/>
 		      </Tab>)}
 		</TabGroup>
diff --git a/frontend/src/pages/posts/PostHistoryPage.tsx b/frontend/src/pages/posts/PostHistoryPage.tsx
index fb6b27e..564ed79 100644
--- a/frontend/src/pages/posts/PostHistoryPage.tsx
+++ b/frontend/src/pages/posts/PostHistoryPage.tsx
@@ -95,6 +95,8 @@ export default (() => {
 		    <col className="w-96"/>
 		    {/* タグ */}
 		    <col className="w-[48rem]"/>
+		    {/* 親投稿 */}
+		    <col className="w-[48rem]"/>
 		    {/* オリジナルの投稿日時 */}
 		    <col className="w-96"/>
 		    {/* 更新日時 */}
@@ -110,6 +112,7 @@ export default (() => {
 		      <th className="p-2 text-left">タイトル</th>
 		      <th className="p-2 text-left">URL</th>
 		      <th className="p-2 text-left">タグ</th>
+		      <th className="p-2 text-left">親投稿</th>
 		      <th className="p-2 text-left">オリジナルの投稿日時</th>
 		      <th className="p-2 text-left">更新日時</th>
 		      <th className="p-2"/>
@@ -180,6 +183,28 @@ export default (() => {
 					    {tag.name}
 					  </span>))))}
 			    </td>
+			    <td className="p-2">
+			      {change.parentPosts.map ((pp, i) => (
+				  pp.type === 'added'
+				  ? (
+				      <ins
+					  key={i}
+					  className="mr-2 text-green-600 dark:text-green-400">
+					{pp.title}
+				      </ins>)
+				  : (
+				      pp.type === 'removed'
+				      ? (
+					  <del
+					      key={i}
+					      className="mr-2 text-red-600 dark:text-red-400">
+					    {pp.title}
+					  </del>)
+				      : (
+					  <span key={i} className="mr-2">
+					    {pp.title}
+					  </span>))))}
+			    </td>
 			    <td className="p-2">
 			      {change.versionNo === 1
 			       ? originalCreatedAtString (change.originalCreatedFrom.current,
@@ -225,6 +250,8 @@ export default (() => {
 						  .map (t => t.name)
 						  .filter (t => t.slice (0, 5) !== 'nico:')
 						  .join (' '),
+					    parent_post_ids:
+						change.parentPosts.map (p => p.id).join (' '),
 					    original_created_from:
 						change.originalCreatedFrom.current,
 					    original_created_before:
diff --git a/frontend/src/pages/posts/PostNewPage.tsx b/frontend/src/pages/posts/PostNewPage.tsx
index 5a2f77b..a5bcbf3 100644
--- a/frontend/src/pages/posts/PostNewPage.tsx
+++ b/frontend/src/pages/posts/PostNewPage.tsx
@@ -29,6 +29,7 @@ export default (({ user }: Props) => {
 
   const [originalCreatedBefore, setOriginalCreatedBefore] = useState<string | null> (null)
   const [originalCreatedFrom, setOriginalCreatedFrom] = useState<string | null> (null)
+  const [parentPostIds, setParentPostIds] = useState ('')
   const [tags, setTags] = useState ('')
   const [thumbnailAutoFlg, setThumbnailAutoFlg] = useState (true)
   const [thumbnailFile, setThumbnailFile] = useState<File | null> (null)
@@ -46,6 +47,7 @@ export default (({ user }: Props) => {
     formData.append ('title', title)
     formData.append ('url', url)
     formData.append ('tags', tags)
+    formData.append ('parent_post_ids', parentPostIds)
     if (thumbnailFile)
       formData.append ('thumbnail', thumbnailFile)
     if (originalCreatedFrom)
@@ -177,6 +179,16 @@ export default (({ user }: Props) => {
 		     className="mt-2 max-h-48 rounded border"/>)}
 	  </div>
 
+	  {/* 親投稿 */}
+	  <div>
+	    <Label>親投稿</Label>
+	    <input
+		type="text"
+		value={parentPostIds}
+		onChange={e => setParentPostIds (e.target.value)}
+		className="w-full border p-2 rounded"/>
+	  </div>
+
 	  {/* タグ */}
 	  <PostFormTagsArea tags={tags} setTags={setTags}/>
 
diff --git a/frontend/src/types.ts b/frontend/src/types.ts
index d5eb53e..51363c3 100644
--- a/frontend/src/types.ts
+++ b/frontend/src/types.ts
@@ -121,6 +121,9 @@ export type Post = {
     thumbnail:              string | null
     thumbnailBase:          string | null
     tags:                   Tag[]
+    parentPosts?:           Post[]
+    childPosts?:            Post[]
+    siblingPosts?:          Record<`${ number }`, Post[]>
     viewed:                 boolean
     related:                Post[]
     originalCreatedFrom:    string | null
@@ -144,7 +147,11 @@ export type PostVersion = {
     url:                    { current: string; prev: string | null }
     thumbnail:              { current: string | null; prev: string | null }
     thumbnailBase:          { current: string | null; prev: string | null }
-    tags:                   { name: string; type: 'context' | 'added' | 'removed' }[]
+    tags:                   { name: string
+			      type: 'context' | 'added' | 'removed' }[]
+    parentPosts:            { id: number
+			      title: string
+			      type: 'context' | 'added' | 'removed' }[]
     originalCreatedFrom:    { current: string | null; prev: string | null }
     originalCreatedBefore:  { current: string | null; prev: string | null }
     createdAt:              string