diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index 310c449..3c15d7c 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -127,7 +127,7 @@ class PostsController < ApplicationController
 
     post = Post.new(title:, url:, thumbnail_base: nil, uploaded_user: current_user,
                     original_created_from:, original_created_before:)
-    post.thumbnail.attach(thumbnail)
+    post.thumbnail.attach(thumbnail) if thumbnail.present?
 
     ApplicationRecord.transaction do
       post.save!
@@ -149,8 +149,8 @@ class PostsController < ApplicationController
     render json: PostRepr.base(post), status: :created
   rescue ArgumentError => e
     render json: { errors: [e.message] }, status: :unprocessable_entity
-  rescue ActiveRecord::RecordInvalid
-    render json: { errors: post.errors.full_messages }, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   rescue Tag::NicoTagNormalisationError
     head :bad_request
   end
@@ -204,8 +204,8 @@ class PostsController < ApplicationController
     render json:, status: :ok
   rescue ArgumentError => e
     render json: { errors: [e.message] }, status: :unprocessable_entity
-  rescue ActiveRecord::RecordInvalid
-    render json: post.errors, status: :unprocessable_entity
+  rescue ActiveRecord::RecordInvalid => e
+    render json: { errors: e.record.errors.full_messages }, status: :unprocessable_entity
   rescue Tag::NicoTagNormalisationError
     head :bad_request
   end
diff --git a/backend/app/models/post.rb b/backend/app/models/post.rb
index 02b4c08..d036fae 100644
--- a/backend/app/models/post.rb
+++ b/backend/app/models/post.rb
@@ -56,7 +56,7 @@ class Post < ApplicationRecord
 
   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).pluck(:parent_post_id)
+  def snapshot_parent_post_ids = parents.order(:id).pluck(:id)
 
   def related limit: nil
     ids = post_similarities.order(cos: :desc)
diff --git a/frontend/src/components/PostEditForm.tsx b/frontend/src/components/PostEditForm.tsx
index 5558e69..f584117 100644
--- a/frontend/src/components/PostEditForm.tsx
+++ b/frontend/src/components/PostEditForm.tsx
@@ -52,6 +52,9 @@ export default (({ post, onSave }: Props) => {
       onSave ({ ...post,
 		title:                  data.title,
 		tags:                   data.tags,
+		parentPosts:            data.parentPosts,
+		childPosts:             data.childPosts,
+		siblingPosts:           data.siblingPosts,
 		originalCreatedFrom:    data.originalCreatedFrom,
 		originalCreatedBefore:  data.originalCreatedBefore } as Post)
       toast ({ description: '更新しました．' })
diff --git a/frontend/src/components/PostList.tsx b/frontend/src/components/PostList.tsx
index 582762e..8bd6118 100644
--- a/frontend/src/components/PostList.tsx
+++ b/frontend/src/components/PostList.tsx
@@ -42,8 +42,8 @@ export default (({ posts, onClick }: Props) => {
 		    layoutId={layoutId}
 		    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')}
+				   (post.childPosts ?? []).length > 0 && 'outline-4 border-green-500',
+				   (post.parentPosts ?? []).length > 0 && 'outline-4 border-yellow-500')}
 		    whileHover={{ scale: 1.02 }}
 		    onLayoutAnimationStart={() => {
 		      if (!(cardRef.current))
diff --git a/frontend/src/pages/posts/PostHistoryPage.tsx b/frontend/src/pages/posts/PostHistoryPage.tsx
index 564ed79..825efe9 100644
--- a/frontend/src/pages/posts/PostHistoryPage.tsx
+++ b/frontend/src/pages/posts/PostHistoryPage.tsx
@@ -95,8 +95,8 @@ export default (() => {
 		    <col className="w-96"/>
 		    {/* タグ */}
 		    <col className="w-[48rem]"/>
-		    {/* 親投稿 */}
-		    <col className="w-[48rem]"/>
+		    {/* TODO: 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 */}
@@ -112,7 +112,8 @@ 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>
+		      {/* TODO: 親投稿の履歴 */}
+		      {/* <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"/>
@@ -183,7 +184,8 @@ export default (() => {
 					    {tag.name}
 					  </span>))))}
 			    </td>
-			    <td className="p-2">
+			    {/* TODO: 親投稿の履歴 */}
+			    {/* <td className="p-2">
 			      {change.parentPosts.map ((pp, i) => (
 				  pp.type === 'added'
 				  ? (
@@ -204,7 +206,7 @@ export default (() => {
 					  <span key={i} className="mr-2">
 					    {pp.title}
 					  </span>))))}
-			    </td>
+			    </td> */}
 			    <td className="p-2">
 			      {change.versionNo === 1
 			       ? originalCreatedAtString (change.originalCreatedFrom.current,
@@ -251,7 +253,10 @@ export default (() => {
 						  .filter (t => t.slice (0, 5) !== 'nico:')
 						  .join (' '),
 					    parent_post_ids:
-						change.parentPosts.map (p => p.id).join (' '),
+						change.parentPosts
+						.filter (p => p.type !== 'removed')
+						.map (p => p.id)
+						.join (' '),
 					    original_created_from:
 						change.originalCreatedFrom.current,
 					    original_created_before: