diff --git a/CHANGELOG.md b/CHANGELOG.md
index c815e65ab39069295ba6f82206d1e26d43e0bf4d..4d8c8ded3a9ceddc86fb249fcb61c3eaeab9d34c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,7 @@
 ## Unreleased
 
 ### General
--
+- Feat: コンテンツの表示にログインを必須にできるように
 
 ### Client
 - Enhance: Bull DashboardでRelationship Queueの状態も確認できるように  
diff --git a/locales/index.d.ts b/locales/index.d.ts
index fb010d9353e2359bc7a1450f40f6141b32e72d6a..e00254030746d733745c32cfbdee81e5f2c7b2b6 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -5190,6 +5190,32 @@ export interface Locale extends ILocale {
      * 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。
      */
     "yourNameContainsProhibitedWordsDescription": string;
+    /**
+     * 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
+     */
+    "thisContentsAreMarkedAsSigninRequiredByAuthor": string;
+    /**
+     * ロックダウン
+     */
+    "lockdown": string;
+    "_accountSettings": {
+        /**
+         * コンテンツの表示にログインを必須にする
+         */
+        "requireSigninToViewContents": string;
+        /**
+         * あなたが作成した全てのノートなどのコンテンツを表示するのにログインを必須にします。クローラーから情報を収集されるのを防ぐ効果が期待できます。
+         */
+        "requireSigninToViewContentsDescription1": string;
+        /**
+         * URLプレビュー(OGP)、Webページへの埋め込み、ノートの引用に対応していないサーバーからの表示も不可になります。
+         */
+        "requireSigninToViewContentsDescription2": string;
+        /**
+         * リモートサーバーに連合されたコンテンツでは、これらの制限が適用されない場合があります。
+         */
+        "requireSigninToViewContentsDescription3": string;
+    };
     "_abuseUserReport": {
         /**
          * 転送
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index c241a9e5602a6a614b82c84cd99d0d265e388890..f3f7e5c77f0ea0f9a1add704b9821a36384966ec 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -1293,6 +1293,14 @@ 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。"
 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"
+lockdown: "ロックダウン"
+
+_accountSettings:
+  requireSigninToViewContents: "コンテンツの表示にログインを必須にする"
+  requireSigninToViewContentsDescription1: "あなたが作成した全てのノートなどのコンテンツを表示するのにログインを必須にします。クローラーから情報を収集されるのを防ぐ効果が期待できます。"
+  requireSigninToViewContentsDescription2: "URLプレビュー(OGP)、Webページへの埋め込み、ノートの引用に対応していないサーバーからの表示も不可になります。"
+  requireSigninToViewContentsDescription3: "リモートサーバーに連合されたコンテンツでは、これらの制限が適用されない場合があります。"
 
 _abuseUserReport:
   forward: "転送"
diff --git a/packages/backend/migration/1729333924409-signinRequiredForShowContents.js b/packages/backend/migration/1729333924409-signinRequiredForShowContents.js
new file mode 100644
index 0000000000000000000000000000000000000000..5d4d1fcce2fde4c5e7456ce8a53d9966a51e494d
--- /dev/null
+++ b/packages/backend/migration/1729333924409-signinRequiredForShowContents.js
@@ -0,0 +1,16 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class SigninRequiredForShowContents1729333924409 {
+    name = 'SigninRequiredForShowContents1729333924409'
+
+    async up(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "user" ADD "requireSigninToViewContents" boolean NOT NULL DEFAULT false`);
+    }
+
+    async down(queryRunner) {
+        await queryRunner.query(`ALTER TABLE "user" DROP COLUMN "requireSigninToViewContents"`);
+    }
+}
diff --git a/packages/backend/src/core/WebhookTestService.ts b/packages/backend/src/core/WebhookTestService.ts
index 55c8a527050cb74c0b738994615f69c7e533d087..254d961040f0d2afd0ae0b47299ffea00665a2d1 100644
--- a/packages/backend/src/core/WebhookTestService.ts
+++ b/packages/backend/src/core/WebhookTestService.ts
@@ -83,6 +83,7 @@ function generateDummyUser(override?: Partial<MiUser>): MiUser {
 		isExplorable: true,
 		isHibernated: false,
 		isDeleted: false,
+		requireSigninToViewContents: false,
 		emojis: [],
 		score: 0,
 		host: null,
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index fba8947f032773cabb19e071dfbf08e229947d56..8235d7ba303d2054aa861e02fecbb1756f980c5f 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -495,6 +495,7 @@ export class ApRendererService {
 			summary: profile.description ? this.mfmService.toHtml(mfm.parse(profile.description)) : null,
 			_misskey_summary: profile.description,
 			_misskey_followedMessage: profile.followedMessage,
+			_misskey_requireSigninToViewContents: user.requireSigninToViewContents,
 			icon: avatar ? this.renderImage(avatar) : null,
 			image: banner ? this.renderImage(banner) : null,
 			tag,
diff --git a/packages/backend/src/core/activitypub/misc/contexts.ts b/packages/backend/src/core/activitypub/misc/contexts.ts
index 3dd85b9b86c58cee0ea753731bc40aed622800b5..447f7ef3db60f67dff2d2826992c687599d9dc2b 100644
--- a/packages/backend/src/core/activitypub/misc/contexts.ts
+++ b/packages/backend/src/core/activitypub/misc/contexts.ts
@@ -555,6 +555,7 @@ const extension_context_definition = {
 	'_misskey_votes': 'misskey:_misskey_votes',
 	'_misskey_summary': 'misskey:_misskey_summary',
 	'_misskey_followedMessage': 'misskey:_misskey_followedMessage',
+	'_misskey_requireSigninToViewContents': 'misskey:_misskey_requireSigninToViewContents',
 	'isCat': 'misskey:isCat',
 	// vcard
 	vcard: 'http://www.w3.org/2006/vcard/ns#',
diff --git a/packages/backend/src/core/activitypub/models/ApPersonService.ts b/packages/backend/src/core/activitypub/models/ApPersonService.ts
index 73281078e530be3345957bf31a7d841fed37a886..c7915ed94fe982b2acf3f2c6d4c9a5448d78fcae 100644
--- a/packages/backend/src/core/activitypub/models/ApPersonService.ts
+++ b/packages/backend/src/core/activitypub/models/ApPersonService.ts
@@ -356,6 +356,7 @@ export class ApPersonService implements OnModuleInit {
 					tags,
 					isBot,
 					isCat: (person as any).isCat === true,
+					requireSigninToViewContents: (person as any).requireSigninToViewContents === true,
 					emojis,
 				})) as MiRemoteUser;
 
diff --git a/packages/backend/src/core/activitypub/type.ts b/packages/backend/src/core/activitypub/type.ts
index 154965b9d592ee1838a0176f2b4503ae1278385a..8a860335faf339b0704cc7ad4674801acab31dcb 100644
--- a/packages/backend/src/core/activitypub/type.ts
+++ b/packages/backend/src/core/activitypub/type.ts
@@ -14,6 +14,7 @@ export interface IObject {
 	summary?: string;
 	_misskey_summary?: string;
 	_misskey_followedMessage?: string | null;
+	_misskey_requireSigninToViewContents?: boolean;
 	published?: string;
 	cc?: ApObject;
 	to?: ApObject;
diff --git a/packages/backend/src/core/entities/NoteEntityService.ts b/packages/backend/src/core/entities/NoteEntityService.ts
index 3e1f094fce594f17bef152f49d3429d8aa2d4976..62016936a2633fa1e315369ca64e9da55d06f5cc 100644
--- a/packages/backend/src/core/entities/NoteEntityService.ts
+++ b/packages/backend/src/core/entities/NoteEntityService.ts
@@ -149,6 +149,10 @@ export class NoteEntityService implements OnModuleInit {
 			}
 		}
 
+		if (packedNote.user.requireSigninToViewContents && meId == null) {
+			hide = true;
+		}
+
 		if (hide) {
 			packedNote.visibleUserIds = undefined;
 			packedNote.fileIds = [];
diff --git a/packages/backend/src/core/entities/UserEntityService.ts b/packages/backend/src/core/entities/UserEntityService.ts
index c9939adf11371f45be8429da7280bfa50d2dfdec..747ffc780f5dcca52f401c44a04a2c00a0bfce91 100644
--- a/packages/backend/src/core/entities/UserEntityService.ts
+++ b/packages/backend/src/core/entities/UserEntityService.ts
@@ -490,6 +490,7 @@ export class UserEntityService implements OnModuleInit {
 			}))) : [],
 			isBot: user.isBot,
 			isCat: user.isCat,
+			requireSigninToViewContents: user.requireSigninToViewContents === false ? undefined : true,
 			instance: user.host ? this.federatedInstanceService.federatedInstanceCache.fetch(user.host).then(instance => instance ? {
 				name: instance.name,
 				softwareName: instance.softwareName,
diff --git a/packages/backend/src/models/User.ts b/packages/backend/src/models/User.ts
index 805a1e75aebddd3a7e31a683be3c1adc04d8ca51..6fcff77854d22f1fef17472360ab93882d9cfd4c 100644
--- a/packages/backend/src/models/User.ts
+++ b/packages/backend/src/models/User.ts
@@ -202,6 +202,11 @@ export class MiUser {
 	})
 	public isHibernated: boolean;
 
+	@Column('boolean', {
+		default: false,
+	})
+	public requireSigninToViewContents: boolean;
+
 	// アカウントが削除されたかどうかのフラグだが、完全に削除される際は物理削除なので実質削除されるまでの「削除が進行しているかどうか」のフラグ
 	@Column('boolean', {
 		default: false,
diff --git a/packages/backend/src/models/json-schema/user.ts b/packages/backend/src/models/json-schema/user.ts
index 9cffd680f29b73dad42a1da1752f63cd729d7b27..817f8e9292433b1f78ad9e825ad05ddfc8960d51 100644
--- a/packages/backend/src/models/json-schema/user.ts
+++ b/packages/backend/src/models/json-schema/user.ts
@@ -115,6 +115,10 @@ export const packedUserLiteSchema = {
 			type: 'boolean',
 			nullable: false, optional: true,
 		},
+		requireSigninToViewContents: {
+			type: 'boolean',
+			nullable: false, optional: true,
+		},
 		instance: {
 			type: 'object',
 			nullable: false, optional: true,
diff --git a/packages/backend/src/server/api/GetterService.ts b/packages/backend/src/server/api/GetterService.ts
index bff3ab96f33cda2e64ddf5fb05382e45764e9d5b..444e6db744a60b197e72634c04af88171fd96032 100644
--- a/packages/backend/src/server/api/GetterService.ts
+++ b/packages/backend/src/server/api/GetterService.ts
@@ -39,6 +39,17 @@ export class GetterService {
 		return note;
 	}
 
+	@bindThis
+	public async getNoteWithUser(noteId: MiNote['id']) {
+		const note = await this.notesRepository.findOne({ where: { id: noteId }, relations: ['user'] });
+
+		if (note == null) {
+			throw new IdentifiableError('9725d0ce-ba28-4dde-95a7-2cbb2c15de24', 'No such note.');
+		}
+
+		return note;
+	}
+
 	/**
 	 * Get user for API processing
 	 */
diff --git a/packages/backend/src/server/api/endpoints/i/update.ts b/packages/backend/src/server/api/endpoints/i/update.ts
index 0b35005a87c175ff55f43fb4c904f72bb9d6c87c..6680c96f3f2dfe519205b4e3411b5241672cdf89 100644
--- a/packages/backend/src/server/api/endpoints/i/update.ts
+++ b/packages/backend/src/server/api/endpoints/i/update.ts
@@ -179,6 +179,7 @@ export const paramDef = {
 		autoAcceptFollowed: { type: 'boolean' },
 		noCrawle: { type: 'boolean' },
 		preventAiLearning: { type: 'boolean' },
+		requireSigninToViewContents: { type: 'boolean' },
 		isBot: { type: 'boolean' },
 		isCat: { type: 'boolean' },
 		injectFeaturedNote: { type: 'boolean' },
@@ -334,6 +335,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 			if (typeof ps.autoAcceptFollowed === 'boolean') profileUpdates.autoAcceptFollowed = ps.autoAcceptFollowed;
 			if (typeof ps.noCrawle === 'boolean') profileUpdates.noCrawle = ps.noCrawle;
 			if (typeof ps.preventAiLearning === 'boolean') profileUpdates.preventAiLearning = ps.preventAiLearning;
+			if (typeof ps.requireSigninToViewContents === 'boolean') updates.requireSigninToViewContents = ps.requireSigninToViewContents;
 			if (typeof ps.isCat === 'boolean') updates.isCat = ps.isCat;
 			if (typeof ps.injectFeaturedNote === 'boolean') profileUpdates.injectFeaturedNote = ps.injectFeaturedNote;
 			if (typeof ps.receiveAnnouncementEmail === 'boolean') profileUpdates.receiveAnnouncementEmail = ps.receiveAnnouncementEmail;
diff --git a/packages/backend/src/server/api/endpoints/notes/show.ts b/packages/backend/src/server/api/endpoints/notes/show.ts
index adcda30a7d88ac16f19ad5b0a70fbf31e76d5f5a..11839bce36604ab89713830c81dd623ddc51d4b2 100644
--- a/packages/backend/src/server/api/endpoints/notes/show.ts
+++ b/packages/backend/src/server/api/endpoints/notes/show.ts
@@ -26,6 +26,12 @@ export const meta = {
 			code: 'NO_SUCH_NOTE',
 			id: '24fcbfc6-2e37-42b6-8388-c29b3861a08d',
 		},
+
+		signinRequired: {
+			message: 'Signin required.',
+			code: 'SIGNIN_REQUIRED',
+			id: '8e75455b-738c-471d-9f80-62693f33372e',
+		},
 	},
 } as const;
 
@@ -44,11 +50,15 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 		private getterService: GetterService,
 	) {
 		super(meta, paramDef, async (ps, me) => {
-			const note = await this.getterService.getNote(ps.noteId).catch(err => {
+			const note = await this.getterService.getNoteWithUser(ps.noteId).catch(err => {
 				if (err.id === '9725d0ce-ba28-4dde-95a7-2cbb2c15de24') throw new ApiError(meta.errors.noSuchNote);
 				throw err;
 			});
 
+			if (note.user!.requireSigninToViewContents && me == null) {
+				throw new ApiError(meta.errors.signinRequired);
+			}
+
 			return await this.noteEntityService.pack(note, me, {
 				detail: true,
 			});
diff --git a/packages/backend/src/server/api/endpoints/users/notes.ts b/packages/backend/src/server/api/endpoints/users/notes.ts
index 7fc11ba369057146f4c5460f317e504c15b0d775..e9c334057e763730fcb11aa99fee1492233272d2 100644
--- a/packages/backend/src/server/api/endpoints/users/notes.ts
+++ b/packages/backend/src/server/api/endpoints/users/notes.ts
@@ -42,6 +42,12 @@ export const meta = {
 			code: 'BOTH_WITH_REPLIES_AND_WITH_FILES',
 			id: '91c8cb9f-36ed-46e7-9ca2-7df96ed6e222',
 		},
+
+		signinRequired: {
+			message: 'Signin required.',
+			code: 'SIGNIN_REQUIRED',
+			id: 'd1588a9e-4b4d-4c07-807f-16f1486577a2',
+		},
 	},
 } as const;
 
diff --git a/packages/backend/src/server/web/ClientServerService.ts b/packages/backend/src/server/web/ClientServerService.ts
index c9c29e42a8c8cb2a72b98604319502363925bb85..4860ef3e12c5adce07e52c0e4c74d5edd7ccb8b6 100644
--- a/packages/backend/src/server/web/ClientServerService.ts
+++ b/packages/backend/src/server/web/ClientServerService.ts
@@ -601,12 +601,15 @@ export class ClientServerService {
 		fastify.get<{ Params: { note: string; } }>('/notes/:note', async (request, reply) => {
 			vary(reply.raw, 'Accept');
 
-			const note = await this.notesRepository.findOneBy({
-				id: request.params.note,
-				visibility: In(['public', 'home']),
+			const note = await this.notesRepository.findOne({
+				where: {
+					id: request.params.note,
+					visibility: In(['public', 'home']),
+				},
+				relations: ['user'],
 			});
 
-			if (note) {
+			if (note && !note.user!.requireSigninToViewContents) {
 				const _note = await this.noteEntityService.pack(note);
 				const profile = await this.userProfilesRepository.findOneByOrFail({ userId: note.userId });
 				reply.header('Cache-Control', 'public, max-age=15');
diff --git a/packages/frontend/src/components/MkFollowButton.vue b/packages/frontend/src/components/MkFollowButton.vue
index ccea7cd453b15464c38dac43ac547ec39c229b1e..cc07175907901bd142504b9015dfbd0d613d21e9 100644
--- a/packages/frontend/src/components/MkFollowButton.vue
+++ b/packages/frontend/src/components/MkFollowButton.vue
@@ -37,13 +37,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 <script lang="ts" setup>
 import { onBeforeUnmount, onMounted, ref } from 'vue';
 import * as Misskey from 'misskey-js';
+import { host } from '@@/js/config.js';
 import * as os from '@/os.js';
 import { misskeyApi } from '@/scripts/misskey-api.js';
 import { useStream } from '@/stream.js';
 import { i18n } from '@/i18n.js';
 import { claimAchievement } from '@/scripts/achievements.js';
 import { pleaseLogin } from '@/scripts/please-login.js';
-import { host } from '@@/js/config.js';
 import { $i } from '@/account.js';
 import { defaultStore } from '@/store.js';
 
@@ -80,7 +80,7 @@ function onFollowChange(user: Misskey.entities.UserDetailed) {
 }
 
 async function onClick() {
-	pleaseLogin(undefined, { type: 'web', path: `/@${props.user.username}@${props.user.host ?? host}` });
+	pleaseLogin({ openOnRemote: { type: 'web', path: `/@${props.user.username}@${props.user.host ?? host}` } });
 
 	wait.value = true;
 
diff --git a/packages/frontend/src/components/MkNote.vue b/packages/frontend/src/components/MkNote.vue
index 828ad2e872b6ee839aba93c10c01b9ddf905afb7..425c4992da0009c0575ac2cb47869726d87e3d31 100644
--- a/packages/frontend/src/components/MkNote.vue
+++ b/packages/frontend/src/components/MkNote.vue
@@ -419,7 +419,7 @@ if (!props.mock) {
 }
 
 function renote(viaKeyboard = false) {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	showMovedDialog();
 
 	const { menu } = getRenoteMenu({ note: note.value, renoteButton, mock: props.mock });
@@ -429,7 +429,7 @@ function renote(viaKeyboard = false) {
 }
 
 function reply(): void {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	if (props.mock) {
 		return;
 	}
@@ -442,7 +442,7 @@ function reply(): void {
 }
 
 function react(): void {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	showMovedDialog();
 	if (appearNote.value.reactionAcceptance === 'likeOnly') {
 		sound.playMisskeySfx('reaction');
@@ -563,7 +563,7 @@ function showRenoteMenu(): void {
 	}
 
 	if (isMyRenote) {
-		pleaseLogin(undefined, pleaseLoginContext.value);
+		pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 		os.popupMenu([
 			getCopyNoteLinkMenu(note.value, i18n.ts.copyLinkRenote),
 			{ type: 'divider' },
diff --git a/packages/frontend/src/components/MkNoteDetailed.vue b/packages/frontend/src/components/MkNoteDetailed.vue
index 6d53685651b7e973f8225a10617075c38d25f12d..e0473dce5e13ac7eef4bd9328bb9487d015d5cd8 100644
--- a/packages/frontend/src/components/MkNoteDetailed.vue
+++ b/packages/frontend/src/components/MkNoteDetailed.vue
@@ -207,6 +207,7 @@ import { computed, inject, onMounted, provide, ref, shallowRef } from 'vue';
 import * as mfm from 'mfm-js';
 import * as Misskey from 'misskey-js';
 import { isLink } from '@@/js/is-link.js';
+import { host } from '@@/js/config.js';
 import MkNoteSub from '@/components/MkNoteSub.vue';
 import MkNoteSimple from '@/components/MkNoteSimple.vue';
 import MkReactionsViewer from '@/components/MkReactionsViewer.vue';
@@ -230,7 +231,6 @@ import { reactionPicker } from '@/scripts/reaction-picker.js';
 import { extractUrlFromMfm } from '@/scripts/extract-url-from-mfm.js';
 import { $i } from '@/account.js';
 import { i18n } from '@/i18n.js';
-import { host } from '@@/js/config.js';
 import { getNoteClipMenu, getNoteMenu, getRenoteMenu } from '@/scripts/get-note-menu.js';
 import { useNoteCapture } from '@/scripts/use-note-capture.js';
 import { deepClone } from '@/scripts/clone.js';
@@ -404,7 +404,7 @@ if (appearNote.value.reactionAcceptance === 'likeOnly') {
 }
 
 function renote() {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	showMovedDialog();
 
 	const { menu } = getRenoteMenu({ note: note.value, renoteButton });
@@ -412,7 +412,7 @@ function renote() {
 }
 
 function reply(): void {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	showMovedDialog();
 	os.post({
 		reply: appearNote.value,
@@ -423,7 +423,7 @@ function reply(): void {
 }
 
 function react(): void {
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	showMovedDialog();
 	if (appearNote.value.reactionAcceptance === 'likeOnly') {
 		sound.playMisskeySfx('reaction');
@@ -499,7 +499,7 @@ async function clip(): Promise<void> {
 
 function showRenoteMenu(): void {
 	if (!isMyRenote) return;
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 	os.popupMenu([{
 		text: i18n.ts.unrenote,
 		icon: 'ti ti-trash',
diff --git a/packages/frontend/src/components/MkPoll.vue b/packages/frontend/src/components/MkPoll.vue
index 48913004e04c7ea440acab1f2f834ca2a54c2433..e70ac7ff1a00d787e774cdea1e6b6fbecdd2e534 100644
--- a/packages/frontend/src/components/MkPoll.vue
+++ b/packages/frontend/src/components/MkPoll.vue
@@ -29,14 +29,14 @@ SPDX-License-Identifier: AGPL-3.0-only
 <script lang="ts" setup>
 import { computed, ref } from 'vue';
 import * as Misskey from 'misskey-js';
+import { host } from '@@/js/config.js';
+import { useInterval } from '@@/js/use-interval.js';
 import type { OpenOnRemoteOptions } from '@/scripts/please-login.js';
 import { sum } from '@/scripts/array.js';
 import { pleaseLogin } from '@/scripts/please-login.js';
 import * as os from '@/os.js';
 import { misskeyApi } from '@/scripts/misskey-api.js';
 import { i18n } from '@/i18n.js';
-import { host } from '@@/js/config.js';
-import { useInterval } from '@@/js/use-interval.js';
 
 const props = defineProps<{
 	noteId: string;
@@ -85,7 +85,7 @@ if (props.poll.expiresAt) {
 const vote = async (id) => {
 	if (props.readOnly || closed.value || isVoted.value) return;
 
-	pleaseLogin(undefined, pleaseLoginContext.value);
+	pleaseLogin({ openOnRemote: pleaseLoginContext.value });
 
 	const { canceled } = await os.confirm({
 		type: 'question',
diff --git a/packages/frontend/src/os.ts b/packages/frontend/src/os.ts
index 4d41cf5bc0995a03a09b93312819796b0cda0a54..07d91a0644e9bfb92bc2ae03132aafcd75165854 100644
--- a/packages/frontend/src/os.ts
+++ b/packages/frontend/src/os.ts
@@ -688,14 +688,16 @@ export function contextMenu(items: MenuItem[], ev: MouseEvent): Promise<void> {
 }
 
 export function post(props: Record<string, any> = {}): Promise<void> {
-	pleaseLogin(undefined, (props.initialText || props.initialNote ? {
-		type: 'share',
-		params: {
-			text: props.initialText ?? props.initialNote.text,
-			visibility: props.initialVisibility ?? props.initialNote?.visibility,
-			localOnly: (props.initialLocalOnly || props.initialNote?.localOnly) ? '1' : '0',
-		},
-	} : undefined));
+	pleaseLogin({
+		openOnRemote: (props.initialText || props.initialNote ? {
+			type: 'share',
+			params: {
+				text: props.initialText ?? props.initialNote.text,
+				visibility: props.initialVisibility ?? props.initialNote?.visibility,
+				localOnly: (props.initialLocalOnly || props.initialNote?.localOnly) ? '1' : '0',
+			},
+		} : undefined),
+	});
 
 	showMovedDialog();
 	return new Promise(resolve => {
diff --git a/packages/frontend/src/pages/not-found.vue b/packages/frontend/src/pages/not-found.vue
index 93a792c42f8cd41c12cae6b54fcc964f97e077a2..6a2d01b6fa663e9b3fc0178c2dbd7bd019393494 100644
--- a/packages/frontend/src/pages/not-found.vue
+++ b/packages/frontend/src/pages/not-found.vue
@@ -24,7 +24,7 @@ const props = defineProps<{
 }>();
 
 if (props.showLoginPopup) {
-	pleaseLogin('/');
+	pleaseLogin({ path: '/' });
 }
 
 const headerActions = computed(() => []);
diff --git a/packages/frontend/src/pages/note.vue b/packages/frontend/src/pages/note.vue
index 448244204d043a340429a66a7cf31c0b5bf85e21..454ee3c6bcf3f241c372bd31cca525ee97cdd08f 100644
--- a/packages/frontend/src/pages/note.vue
+++ b/packages/frontend/src/pages/note.vue
@@ -61,6 +61,7 @@ import { i18n } from '@/i18n.js';
 import { dateString } from '@/filters/date.js';
 import MkClipPreview from '@/components/MkClipPreview.vue';
 import { defaultStore } from '@/store.js';
+import { pleaseLogin } from '@/scripts/please-login.js';
 
 const props = defineProps<{
 	noteId: string;
@@ -128,6 +129,11 @@ function fetchNote() {
 			});
 		}
 	}).catch(err => {
+		if (err.id === '8e75455b-738c-471d-9f80-62693f33372e') {
+			pleaseLogin({
+				message: i18n.ts.thisContentsAreMarkedAsSigninRequiredByAuthor,
+			});
+		}
 		error.value = err;
 	});
 }
diff --git a/packages/frontend/src/pages/settings/privacy.vue b/packages/frontend/src/pages/settings/privacy.vue
index d418be624ef24026baba99ff18a08fb416c34a08..e277dfad71dd6c246b87bf81f04056014ff08881 100644
--- a/packages/frontend/src/pages/settings/privacy.vue
+++ b/packages/frontend/src/pages/settings/privacy.vue
@@ -36,7 +36,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 		<template #caption>{{ i18n.ts.noCrawleDescription }}</template>
 	</MkSwitch>
 	<MkSwitch v-model="preventAiLearning" @update:modelValue="save()">
-		{{ i18n.ts.preventAiLearning }}<span class="_beta">{{ i18n.ts.beta }}</span>
+		{{ i18n.ts.preventAiLearning }}
 		<template #caption>{{ i18n.ts.preventAiLearningDescription }}</template>
 	</MkSwitch>
 	<MkSwitch v-model="isExplorable" @update:modelValue="save()">
@@ -44,6 +44,21 @@ SPDX-License-Identifier: AGPL-3.0-only
 		<template #caption>{{ i18n.ts.makeExplorableDescription }}</template>
 	</MkSwitch>
 
+	<FormSection>
+		<template #label>{{ i18n.ts.lockdown }}</template>
+
+		<div class="_gaps_m">
+			<MkSwitch v-model="requireSigninToViewContents" @update:modelValue="save()">
+				{{ i18n.ts._accountSettings.requireSigninToViewContents }}<span class="_beta">{{ i18n.ts.beta }}</span>
+				<template #caption>
+					<div>{{ i18n.ts._accountSettings.requireSigninToViewContentsDescription1 }}</div>
+					<div><i class="ti ti-alert-triangle" style="color: var(--MI_THEME-warn);"></i> {{ i18n.ts._accountSettings.requireSigninToViewContentsDescription2 }}</div>
+					<div><i class="ti ti-alert-triangle" style="color: var(--MI_THEME-warn);"></i> {{ i18n.ts._accountSettings.requireSigninToViewContentsDescription3 }}</div>
+				</template>
+			</MkSwitch>
+		</div>
+	</FormSection>
+
 	<FormSection>
 		<div class="_gaps_m">
 			<MkSwitch v-model="rememberNoteVisibility" @update:modelValue="save()">{{ i18n.ts.rememberNoteVisibility }}</MkSwitch>
@@ -90,6 +105,7 @@ const autoAcceptFollowed = ref($i.autoAcceptFollowed);
 const noCrawle = ref($i.noCrawle);
 const preventAiLearning = ref($i.preventAiLearning);
 const isExplorable = ref($i.isExplorable);
+const requireSigninToViewContents = ref($i.requireSigninToViewContents ?? false);
 const hideOnlineStatus = ref($i.hideOnlineStatus);
 const publicReactions = ref($i.publicReactions);
 const followingVisibility = ref($i.followingVisibility);
@@ -107,6 +123,7 @@ function save() {
 		noCrawle: !!noCrawle.value,
 		preventAiLearning: !!preventAiLearning.value,
 		isExplorable: !!isExplorable.value,
+		requireSigninToViewContents: !!requireSigninToViewContents.value,
 		hideOnlineStatus: !!hideOnlineStatus.value,
 		publicReactions: !!publicReactions.value,
 		followingVisibility: followingVisibility.value,
diff --git a/packages/frontend/src/scripts/please-login.ts b/packages/frontend/src/scripts/please-login.ts
index 18f05bc7f42855bbbd87a6afab3b4f71870814a1..43dcf1193674ad514eaab082f7e6cd6c96ec16ec 100644
--- a/packages/frontend/src/scripts/please-login.ts
+++ b/packages/frontend/src/scripts/please-login.ts
@@ -44,17 +44,21 @@ export type OpenOnRemoteOptions = {
 	params: Record<string, string>;
 };
 
-export function pleaseLogin(path?: string, openOnRemote?: OpenOnRemoteOptions) {
+export function pleaseLogin(opts: {
+	path?: string;
+	message?: string;
+	openOnRemote?: OpenOnRemoteOptions;
+} = {}) {
 	if ($i) return;
 
 	const { dispose } = popup(defineAsyncComponent(() => import('@/components/MkSigninDialog.vue')), {
 		autoSet: true,
-		message: openOnRemote ? i18n.ts.signinOrContinueOnRemote : i18n.ts.signinRequired,
-		openOnRemote,
+		message: opts.message ?? (opts.openOnRemote ? i18n.ts.signinOrContinueOnRemote : i18n.ts.signinRequired),
+		openOnRemote: opts.openOnRemote,
 	}, {
 		cancelled: () => {
-			if (path) {
-				window.location.href = path;
+			if (opts.path) {
+				window.location.href = opts.path;
 			}
 		},
 		closed: () => dispose(),
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index 698c08826a0677c5f5bb48dff436955e36b05188..8f84aa37ff80f2f69838b17c66978a7a41d9aecf 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -3736,6 +3736,7 @@ export type components = {
         }[];
       isBot?: boolean;
       isCat?: boolean;
+      requireSigninToViewContents?: boolean;
       instance?: {
         name: string | null;
         softwareName: string | null;
@@ -19844,6 +19845,7 @@ export type operations = {
           autoAcceptFollowed?: boolean;
           noCrawle?: boolean;
           preventAiLearning?: boolean;
+          requireSigninToViewContents?: boolean;
           isBot?: boolean;
           isCat?: boolean;
           injectFeaturedNote?: boolean;