diff --git a/locales/index.d.ts b/locales/index.d.ts
index ceb3cc672d..8d757ff579 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -5231,7 +5231,7 @@ export interface Locale extends ILocale {
      */
     "prohibitedWordsForNameOfUser": string;
     /**
-     * このリストに含まれる文字列がユーザーの名前に含まれる場合、ユーザーの名前の変更を拒否します。モデレーター権限を持つユーザーはこの制限の影響を受けません。
+     * このリストに含まれる文字列がユーザーの名前に含まれる場合、ユーザーの名前の変更を拒否します。モデレーター権限を持つユーザーはこの制限の影響を受けません。ユーザー名(username)に対しても全て小文字に置き換えて検査します。
      */
     "prohibitedWordsForNameOfUserDescription": string;
     /**
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 6af846f7ee..161edfe8bb 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -1303,7 +1303,7 @@ messageToFollower: "フォロワーへのメッセージ"
 target: "対象"
 testCaptchaWarning: "CAPTCHAのテストを目的とした機能です。<strong>本番環境で使用しないでください。</strong>"
 prohibitedWordsForNameOfUser: "禁止ワード（ユーザーの名前）"
-prohibitedWordsForNameOfUserDescription: "このリストに含まれる文字列がユーザーの名前に含まれる場合、ユーザーの名前の変更を拒否します。モデレーター権限を持つユーザーはこの制限の影響を受けません。"
+prohibitedWordsForNameOfUserDescription: "このリストに含まれる文字列がユーザーの名前に含まれる場合、ユーザーの名前の変更を拒否します。モデレーター権限を持つユーザーはこの制限の影響を受けません。ユーザー名(username)に対しても全て小文字に置き換えて検査します。"
 yourNameContainsProhibitedWords: "変更しようとした名前に禁止された文字列が含まれています"
 yourNameContainsProhibitedWordsDescription: "名前に禁止されている文字列が含まれています。この名前を使用したい場合は、サーバー管理者にお問い合わせください。"
 thisContentsAreMarkedAsSigninRequiredByAuthor: "投稿者により、表示にはログインが必要と設定されています"
diff --git a/packages/backend/migration/1752502434151-no-action-on-draft-relation.js b/packages/backend/migration/1752502434151-no-action-on-draft-relation.js
new file mode 100644
index 0000000000..e3c63b79c7
--- /dev/null
+++ b/packages/backend/migration/1752502434151-no-action-on-draft-relation.js
@@ -0,0 +1,24 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class NoActionOnDraftRelation1752502434151 {
+    name = 'NoActionOnDraftRelation1752502434151'
+
+    async up(queryRunner) {
+			await queryRunner.query(`ALTER TABLE "note_draft" DROP CONSTRAINT "FK_NOTE_DRAFT_CHANNEL_ID"`);
+			await queryRunner.query(`ALTER TABLE "note_draft" DROP CONSTRAINT "FK_NOTE_DRAFT_USER_ID"`);
+			await queryRunner.query(`ALTER TABLE "note_draft" DROP CONSTRAINT "FK_NOTE_DRAFT_RENOTE_ID"`);
+			await queryRunner.query(`ALTER TABLE "note_draft" DROP CONSTRAINT "FK_NOTE_DRAFT_REPLY_ID"`);
+			await queryRunner.query(`ALTER TABLE "note_draft" ADD CONSTRAINT "FK_e4983f28b4b18b03491536052f5" FOREIGN KEY ("userId") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+    }
+
+    async down(queryRunner) {
+			await queryRunner.query(`ALTER TABLE "note_draft" DROP CONSTRAINT "FK_e4983f28b4b18b03491536052f5"`);
+			await queryRunner.query(`ALTER TABLE "note_draft" ADD CONSTRAINT "FK_NOTE_DRAFT_REPLY_ID" FOREIGN KEY ("replyId") REFERENCES "note"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+			await queryRunner.query(`ALTER TABLE "note_draft" ADD CONSTRAINT "FK_NOTE_DRAFT_RENOTE_ID" FOREIGN KEY ("renoteId") REFERENCES "note"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+			await queryRunner.query(`ALTER TABLE "note_draft" ADD CONSTRAINT "FK_NOTE_DRAFT_USER_ID" FOREIGN KEY ("userId") REFERENCES "user"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+			await queryRunner.query(`ALTER TABLE "note_draft" ADD CONSTRAINT "FK_NOTE_DRAFT_CHANNEL_ID" FOREIGN KEY ("channelId") REFERENCES "channel"("id") ON DELETE CASCADE ON UPDATE NO ACTION`);
+    }
+}
diff --git a/packages/backend/src/core/SignupService.ts b/packages/backend/src/core/SignupService.ts
index 5462cb0b13..a85da62b86 100644
--- a/packages/backend/src/core/SignupService.ts
+++ b/packages/backend/src/core/SignupService.ts
@@ -93,6 +93,11 @@ export class SignupService {
 			if (isPreserved) {
 				throw new Error('USED_USERNAME');
 			}
+
+			const hasProhibitedWords = this.utilityService.isKeyWordIncluded(username.toLowerCase(), this.meta.prohibitedWordsForNameOfUser);
+			if (hasProhibitedWords) {
+				throw new Error('USED_USERNAME');
+			}
 		}
 
 		const keyPair = await new Promise<string[]>((res, rej) =>
diff --git a/packages/backend/src/core/entities/NoteDraftEntityService.ts b/packages/backend/src/core/entities/NoteDraftEntityService.ts
index 26455029d5..3ef8cdaa12 100644
--- a/packages/backend/src/core/entities/NoteDraftEntityService.ts
+++ b/packages/backend/src/core/entities/NoteDraftEntityService.ts
@@ -5,6 +5,7 @@
 
 import { Inject, Injectable } from '@nestjs/common';
 import { ModuleRef } from '@nestjs/core';
+import { EntityNotFoundError } from 'typeorm';
 import { DI } from '@/di-symbols.js';
 import type { Packed } from '@/misc/json-schema.js';
 import { awaitAll } from '@/misc/prelude/await-all.js';
@@ -90,6 +91,17 @@ export class NoteDraftEntityService implements OnModuleInit {
 		const packedFiles = options?._hint_?.packedFiles;
 		const packedUsers = options?._hint_?.packedUsers;
 
+		async function nullIfEntityNotFound<T>(promise: Promise<T>): Promise<T | null> {
+			try {
+				return await promise;
+			} catch (err) {
+				if (err instanceof EntityNotFoundError) {
+					return null;
+				}
+				throw err;
+			}
+		}
+
 		const packed: Packed<'NoteDraft'> = await awaitAll({
 			id: noteDraft.id,
 			createdAt: this.idService.parse(noteDraft.id).date.toISOString(),
@@ -117,15 +129,15 @@ export class NoteDraftEntityService implements OnModuleInit {
 			} : undefined,
 
 			...(opts.detail ? {
-				reply: noteDraft.replyId ? this.noteEntityService.pack(noteDraft.replyId, me, {
+				reply: noteDraft.replyId ? nullIfEntityNotFound(this.noteEntityService.pack(noteDraft.replyId, me, {
 					detail: false,
 					skipHide: opts.skipHide,
-				}) : undefined,
+				})) : undefined,
 
-				renote: noteDraft.renoteId ? this.noteEntityService.pack(noteDraft.renoteId, me, {
+				renote: noteDraft.renoteId ? nullIfEntityNotFound(this.noteEntityService.pack(noteDraft.renoteId, me, {
 					detail: true,
 					skipHide: opts.skipHide,
-				}) : undefined,
+				})) : undefined,
 
 				poll: noteDraft.hasPoll ? {
 					choices: noteDraft.pollChoices,
diff --git a/packages/backend/src/models/NoteDraft.ts b/packages/backend/src/models/NoteDraft.ts
index edae254bb8..39d85e53dc 100644
--- a/packages/backend/src/models/NoteDraft.ts
+++ b/packages/backend/src/models/NoteDraft.ts
@@ -24,8 +24,9 @@ export class MiNoteDraft {
 	})
 	public replyId: MiNote['id'] | null;
 
+	// There is a possibility that replyId is not null but reply is null when the reply note is deleted.
 	@ManyToOne(type => MiNote, {
-		onDelete: 'CASCADE',
+		createForeignKeyConstraints: false,
 	})
 	@JoinColumn()
 	public reply: MiNote | null;
@@ -38,8 +39,9 @@ export class MiNoteDraft {
 	})
 	public renoteId: MiNote['id'] | null;
 
+	// There is a possibility that renoteId is not null but renote is null when the renote note is deleted.
 	@ManyToOne(type => MiNote, {
-		onDelete: 'CASCADE',
+		createForeignKeyConstraints: false,
 	})
 	@JoinColumn()
 	public renote: MiNote | null;
@@ -114,8 +116,10 @@ export class MiNoteDraft {
 	})
 	public channelId: MiChannel['id'] | null;
 
+	// There is a possibility that channelId is not null but channel is null when the channel is deleted.
+	// (deleting channel is not implemented so it's not happening now but may happen in the future)
 	@ManyToOne(type => MiChannel, {
-		onDelete: 'CASCADE',
+		createForeignKeyConstraints: false,
 	})
 	@JoinColumn()
 	public channel: MiChannel | null;
diff --git a/packages/backend/src/models/json-schema/note-draft.ts b/packages/backend/src/models/json-schema/note-draft.ts
index 20c56d0795..504b263a6d 100644
--- a/packages/backend/src/models/json-schema/note-draft.ts
+++ b/packages/backend/src/models/json-schema/note-draft.ts
@@ -51,11 +51,13 @@ export const packedNoteDraftSchema = {
 			type: 'object',
 			optional: true, nullable: true,
 			ref: 'Note',
+			description: 'The reply target note contents if exists. If the reply target has been deleted since the draft was created, this will be null while replyId is not null.',
 		},
 		renote: {
 			type: 'object',
 			optional: true, nullable: true,
 			ref: 'Note',
+			description: 'The renote target note contents if exists. If the renote target has been deleted since the draft was created, this will be null while renoteId is not null.',
 		},
 		visibility: {
 			type: 'string',
diff --git a/packages/frontend/src/components/MkNoteDraftsDialog.vue b/packages/frontend/src/components/MkNoteDraftsDialog.vue
index 7d41740264..5b8211b715 100644
--- a/packages/frontend/src/components/MkNoteDraftsDialog.vue
+++ b/packages/frontend/src/components/MkNoteDraftsDialog.vue
@@ -42,6 +42,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 											</template>
 										</I18n>
 									</div>
+									<div v-else-if="draft.replyId" class="_nowrap">
+										<i class="ti ti-arrow-back-up"></i> <I18n :src="i18n.ts._drafts.replyTo" tag="span">
+											<template #user>
+												{{ i18n.ts.deletedNote }}
+											</template>
+										</I18n>
+									</div>
 									<div v-if="draft.renote && draft.text != null" class="_nowrap">
 										<i class="ti ti-quote"></i> <I18n :src="i18n.ts._drafts.quoteOf" tag="span">
 											<template #user>
@@ -50,6 +57,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 											</template>
 										</I18n>
 									</div>
+									<div v-else-if="draft.renoteId" class="_nowrap">
+										<i class="ti ti-quote"></i> <I18n :src="i18n.ts._drafts.quoteOf" tag="span">
+											<template #user>
+												{{ i18n.ts.deletedNote }}
+											</template>
+										</I18n>
+									</div>
 									<div v-if="draft.channel" class="_nowrap">
 										<i class="ti ti-device-tv"></i> {{ i18n.tsx._drafts.postTo({ channel: draft.channel.name }) }}
 									</div>
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 51e4b4f45d..7594117deb 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -4401,7 +4401,9 @@ export type components = {
              * @example xxxxxxxxxx
              */
             renoteId?: string | null;
+            /** @description The reply target note contents if exists. If the reply target has been deleted since the draft was created, this will be null while replyId is not null. */
             reply?: components['schemas']['Note'] | null;
+            /** @description The renote target note contents if exists. If the renote target has been deleted since the draft was created, this will be null while renoteId is not null. */
             renote?: components['schemas']['Note'] | null;
             /** @enum {string} */
             visibility: 'public' | 'home' | 'followers' | 'specified';