enhance(backend): refine system account (#15530)

* wip

* wip

* wip

* Update SystemAccountService.ts

* Update 1740121393164-system-accounts.js

* Update DeleteAccountService.ts

* wip

* wip

* wip

* wip

* Update 1740121393164-system-accounts.js

* Update RepositoryModule.ts

* wip

* wip

* wip

* Update ApRendererService.ts

* wip

* wip

* Update SystemAccountService.ts

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* add print logs

* ログが長すぎて出てないかもしれない

* fix migration

* refactor

* fix fed-tests

* Update RelayService.ts

* merge

* Update user.test.ts

* chore: emit log

* fix: tweak sleep duration

* fix: exit 1

* fix: wait for misskey processes to become healthy

* fix: longer sleep for user deletion

* fix: make sleep longer again

* デッドロック解消の試み

https://github.com/misskey-dev/misskey/issues/15005

* Revert "デッドロック解消の試み"

This reverts commit 266141f66fb584371bbb56ef7eba04e14bcff94d.

* wip

* Update SystemAccountService.ts

---------

Co-authored-by: おさむのひと <46447427+samunohito@users.noreply.github.com>
Co-authored-by: zyoshoka <107108195+zyoshoka@users.noreply.github.com>

18 files changed, 299 insertions, 287 deletions

diff --git a/packages/backend/src/core/AbuseReportService.ts b/packages/backend/src/core/AbuseReportService.ts
index 0b022d3b08..846d2c8ebd 100644
--- a/packages/backend/src/core/AbuseReportService.ts
+++ b/packages/backend/src/core/AbuseReportService.ts
@@ -10,9 +10,9 @@ import { bindThis } from '@/decorators.js';
 import type { AbuseUserReportsRepository, MiAbuseUserReport, MiUser, UsersRepository } from '@/models/_.js';
 import { AbuseReportNotificationService } from '@/core/AbuseReportNotificationService.js';
 import { QueueService } from '@/core/QueueService.js';
-import { InstanceActorService } from '@/core/InstanceActorService.js';
 import { ApRendererService } from '@/core/activitypub/ApRendererService.js';
 import { ModerationLogService } from '@/core/ModerationLogService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 import { IdService } from './IdService.js';
 
 @Injectable()
@@ -27,7 +27,7 @@ export class AbuseReportService {
 		private idService: IdService,
 		private abuseReportNotificationService: AbuseReportNotificationService,
 		private queueService: QueueService,
-		private instanceActorService: InstanceActorService,
+		private systemAccountService: SystemAccountService,
 		private apRendererService: ApRendererService,
 		private moderationLogService: ModerationLogService,
 	) {
@@ -136,7 +136,7 @@ export class AbuseReportService {
 			forwarded: true,
 		});
 
-		const actor = await this.instanceActorService.getInstanceActor();
+		const actor = await this.systemAccountService.fetch('actor');
 		const targetUser = await this.usersRepository.findOneByOrFail({ id: report.targetUserId });
 
 		const flag = this.apRendererService.renderFlag(actor, targetUser.uri!, report.comment);
diff --git a/packages/backend/src/core/AccountMoveService.ts b/packages/backend/src/core/AccountMoveService.ts
index 24d11f29ff..0fbb9bcd80 100644
--- a/packages/backend/src/core/AccountMoveService.ts
+++ b/packages/backend/src/core/AccountMoveService.ts
@@ -20,10 +20,10 @@ import { ApPersonService } from '@/core/activitypub/models/ApPersonService.js';
 import { ApDeliverManagerService } from '@/core/activitypub/ApDeliverManagerService.js';
 import { ApRendererService } from '@/core/activitypub/ApRendererService.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
-import { ProxyAccountService } from '@/core/ProxyAccountService.js';
 import { FederatedInstanceService } from '@/core/FederatedInstanceService.js';
 import InstanceChart from '@/core/chart/charts/instance.js';
 import PerUserFollowingChart from '@/core/chart/charts/per-user-following.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 
 @Injectable()
 export class AccountMoveService {
@@ -55,12 +55,12 @@ export class AccountMoveService {
 		private apRendererService: ApRendererService,
 		private apDeliverManagerService: ApDeliverManagerService,
 		private globalEventService: GlobalEventService,
-		private proxyAccountService: ProxyAccountService,
 		private perUserFollowingChart: PerUserFollowingChart,
 		private federatedInstanceService: FederatedInstanceService,
 		private instanceChart: InstanceChart,
 		private relayService: RelayService,
 		private queueService: QueueService,
+		private systemAccountService: SystemAccountService,
 	) {
 	}
 
@@ -126,11 +126,11 @@ export class AccountMoveService {
 		}
 
 		// follow the new account
-		const proxy = await this.proxyAccountService.fetch();
+		const proxy = await this.systemAccountService.fetch('proxy');
 		const followings = await this.followingsRepository.findBy({
 			followeeId: src.id,
 			followerHost: IsNull(), // follower is local
-			followerId: proxy ? Not(proxy.id) : undefined,
+			followerId: Not(proxy.id),
 		});
 		const followJobs = followings.map(following => ({
 			from: { id: following.followerId },
@@ -250,10 +250,8 @@ export class AccountMoveService {
 
 		// Have the proxy account follow the new account in the same way as UserListService.push
 		if (this.userEntityService.isRemoteUser(dst)) {
-			const proxy = await this.proxyAccountService.fetch();
-			if (proxy) {
-				this.queueService.createFollowJob([{ from: { id: proxy.id }, to: { id: dst.id } }]);
-			}
+			const proxy = await this.systemAccountService.fetch('proxy');
+			this.queueService.createFollowJob([{ from: { id: proxy.id }, to: { id: dst.id } }]);
 		}
 	}
 
diff --git a/packages/backend/src/core/CoreModule.ts b/packages/backend/src/core/CoreModule.ts
index 734d135648..dc85a23e5b 100644
--- a/packages/backend/src/core/CoreModule.ts
+++ b/packages/backend/src/core/CoreModule.ts
@@ -24,7 +24,6 @@ import { AppLockService } from './AppLockService.js';
 import { AchievementService } from './AchievementService.js';
 import { AvatarDecorationService } from './AvatarDecorationService.js';
 import { CaptchaService } from './CaptchaService.js';
-import { CreateSystemUserService } from './CreateSystemUserService.js';
 import { CustomEmojiService } from './CustomEmojiService.js';
 import { DeleteAccountService } from './DeleteAccountService.js';
 import { DownloadService } from './DownloadService.js';
@@ -37,7 +36,7 @@ import { HashtagService } from './HashtagService.js';
 import { HttpRequestService } from './HttpRequestService.js';
 import { IdService } from './IdService.js';
 import { ImageProcessingService } from './ImageProcessingService.js';
-import { InstanceActorService } from './InstanceActorService.js';
+import { SystemAccountService } from './SystemAccountService.js';
 import { InternalStorageService } from './InternalStorageService.js';
 import { MetaService } from './MetaService.js';
 import { MfmService } from './MfmService.js';
@@ -69,7 +68,6 @@ import { UserSuspendService } from './UserSuspendService.js';
 import { UserAuthService } from './UserAuthService.js';
 import { VideoProcessingService } from './VideoProcessingService.js';
 import { UserWebhookService } from './UserWebhookService.js';
-import { ProxyAccountService } from './ProxyAccountService.js';
 import { UtilityService } from './UtilityService.js';
 import { FileInfoService } from './FileInfoService.js';
 import { SearchService } from './SearchService.js';
@@ -167,7 +165,6 @@ const $AppLockService: Provider = { provide: 'AppLockService', useExisting: AppL
 const $AchievementService: Provider = { provide: 'AchievementService', useExisting: AchievementService };
 const $AvatarDecorationService: Provider = { provide: 'AvatarDecorationService', useExisting: AvatarDecorationService };
 const $CaptchaService: Provider = { provide: 'CaptchaService', useExisting: CaptchaService };
-const $CreateSystemUserService: Provider = { provide: 'CreateSystemUserService', useExisting: CreateSystemUserService };
 const $CustomEmojiService: Provider = { provide: 'CustomEmojiService', useExisting: CustomEmojiService };
 const $DeleteAccountService: Provider = { provide: 'DeleteAccountService', useExisting: DeleteAccountService };
 const $DownloadService: Provider = { provide: 'DownloadService', useExisting: DownloadService };
@@ -180,7 +177,6 @@ const $HashtagService: Provider = { provide: 'HashtagService', useExisting: Hash
 const $HttpRequestService: Provider = { provide: 'HttpRequestService', useExisting: HttpRequestService };
 const $IdService: Provider = { provide: 'IdService', useExisting: IdService };
 const $ImageProcessingService: Provider = { provide: 'ImageProcessingService', useExisting: ImageProcessingService };
-const $InstanceActorService: Provider = { provide: 'InstanceActorService', useExisting: InstanceActorService };
 const $InternalStorageService: Provider = { provide: 'InternalStorageService', useExisting: InternalStorageService };
 const $MetaService: Provider = { provide: 'MetaService', useExisting: MetaService };
 const $MfmService: Provider = { provide: 'MfmService', useExisting: MfmService };
@@ -191,7 +187,7 @@ const $NotePiningService: Provider = { provide: 'NotePiningService', useExisting
 const $NoteReadService: Provider = { provide: 'NoteReadService', useExisting: NoteReadService };
 const $NotificationService: Provider = { provide: 'NotificationService', useExisting: NotificationService };
 const $PollService: Provider = { provide: 'PollService', useExisting: PollService };
-const $ProxyAccountService: Provider = { provide: 'ProxyAccountService', useExisting: ProxyAccountService };
+const $SystemAccountService: Provider = { provide: 'SystemAccountService', useExisting: SystemAccountService };
 const $PushNotificationService: Provider = { provide: 'PushNotificationService', useExisting: PushNotificationService };
 const $QueryService: Provider = { provide: 'QueryService', useExisting: QueryService };
 const $ReactionService: Provider = { provide: 'ReactionService', useExisting: ReactionService };
@@ -318,7 +314,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		AchievementService,
 		AvatarDecorationService,
 		CaptchaService,
-		CreateSystemUserService,
 		CustomEmojiService,
 		DeleteAccountService,
 		DownloadService,
@@ -331,7 +326,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		HttpRequestService,
 		IdService,
 		ImageProcessingService,
-		InstanceActorService,
 		InternalStorageService,
 		MetaService,
 		MfmService,
@@ -342,7 +336,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		NoteReadService,
 		NotificationService,
 		PollService,
-		ProxyAccountService,
+		SystemAccountService,
 		PushNotificationService,
 		QueryService,
 		ReactionService,
@@ -465,7 +459,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$AchievementService,
 		$AvatarDecorationService,
 		$CaptchaService,
-		$CreateSystemUserService,
 		$CustomEmojiService,
 		$DeleteAccountService,
 		$DownloadService,
@@ -478,7 +471,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$HttpRequestService,
 		$IdService,
 		$ImageProcessingService,
-		$InstanceActorService,
 		$InternalStorageService,
 		$MetaService,
 		$MfmService,
@@ -489,7 +481,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$NoteReadService,
 		$NotificationService,
 		$PollService,
-		$ProxyAccountService,
+		$SystemAccountService,
 		$PushNotificationService,
 		$QueryService,
 		$ReactionService,
@@ -613,7 +605,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		AchievementService,
 		AvatarDecorationService,
 		CaptchaService,
-		CreateSystemUserService,
 		CustomEmojiService,
 		DeleteAccountService,
 		DownloadService,
@@ -626,7 +617,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		HttpRequestService,
 		IdService,
 		ImageProcessingService,
-		InstanceActorService,
 		InternalStorageService,
 		MetaService,
 		MfmService,
@@ -637,7 +627,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		NoteReadService,
 		NotificationService,
 		PollService,
-		ProxyAccountService,
+		SystemAccountService,
 		PushNotificationService,
 		QueryService,
 		ReactionService,
@@ -759,7 +749,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$AchievementService,
 		$AvatarDecorationService,
 		$CaptchaService,
-		$CreateSystemUserService,
 		$CustomEmojiService,
 		$DeleteAccountService,
 		$DownloadService,
@@ -772,7 +761,6 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$HttpRequestService,
 		$IdService,
 		$ImageProcessingService,
-		$InstanceActorService,
 		$InternalStorageService,
 		$MetaService,
 		$MfmService,
@@ -783,7 +771,7 @@ const $ApQuestionService: Provider = { provide: 'ApQuestionService', useExisting
 		$NoteReadService,
 		$NotificationService,
 		$PollService,
-		$ProxyAccountService,
+		$SystemAccountService,
 		$PushNotificationService,
 		$QueryService,
 		$ReactionService,
diff --git a/packages/backend/src/core/CreateSystemUserService.ts b/packages/backend/src/core/CreateSystemUserService.ts
deleted file mode 100644
index 7ef75edb3c..0000000000
--- a/packages/backend/src/core/CreateSystemUserService.ts
+++ /dev/null
@@ -1,86 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-import { randomUUID } from 'node:crypto';
-import { Inject, Injectable } from '@nestjs/common';
-import bcrypt from 'bcryptjs';
-import { IsNull, DataSource } from 'typeorm';
-import { genRsaKeyPair } from '@/misc/gen-key-pair.js';
-import { MiUser } from '@/models/User.js';
-import { MiUserProfile } from '@/models/UserProfile.js';
-import { IdService } from '@/core/IdService.js';
-import { MiUserKeypair } from '@/models/UserKeypair.js';
-import { MiUsedUsername } from '@/models/UsedUsername.js';
-import { DI } from '@/di-symbols.js';
-import { generateNativeUserToken } from '@/misc/token.js';
-import { bindThis } from '@/decorators.js';
-
-@Injectable()
-export class CreateSystemUserService {
-	constructor(
-		@Inject(DI.db)
-		private db: DataSource,
-
-		private idService: IdService,
-	) {
-	}
-
-	@bindThis
-	public async createSystemUser(username: string): Promise<MiUser> {
-		const password = randomUUID();
-
-		// Generate hash of password
-		const salt = await bcrypt.genSalt(8);
-		const hash = await bcrypt.hash(password, salt);
-
-		// Generate secret
-		const secret = generateNativeUserToken();
-
-		const keyPair = await genRsaKeyPair();
-
-		let account!: MiUser;
-
-		// Start transaction
-		await this.db.transaction(async transactionalEntityManager => {
-			const exist = await transactionalEntityManager.findOneBy(MiUser, {
-				usernameLower: username.toLowerCase(),
-				host: IsNull(),
-			});
-
-			if (exist) throw new Error('the user is already exists');
-
-			account = await transactionalEntityManager.insert(MiUser, {
-				id: this.idService.gen(),
-				username: username,
-				usernameLower: username.toLowerCase(),
-				host: null,
-				token: secret,
-				isRoot: false,
-				isLocked: true,
-				isExplorable: false,
-				isBot: true,
-			}).then(x => transactionalEntityManager.findOneByOrFail(MiUser, x.identifiers[0]));
-
-			await transactionalEntityManager.insert(MiUserKeypair, {
-				publicKey: keyPair.publicKey,
-				privateKey: keyPair.privateKey,
-				userId: account.id,
-			});
-
-			await transactionalEntityManager.insert(MiUserProfile, {
-				userId: account.id,
-				autoAcceptFollowed: false,
-				password: hash,
-			});
-
-			await transactionalEntityManager.insert(MiUsedUsername, {
-				createdAt: new Date(),
-				username: username.toLowerCase(),
-			});
-		});
-
-		return account;
-	}
-}
diff --git a/packages/backend/src/core/DeleteAccountService.ts b/packages/backend/src/core/DeleteAccountService.ts
index 7f1b8f3efb..483f14ce7f 100644
--- a/packages/backend/src/core/DeleteAccountService.ts
+++ b/packages/backend/src/core/DeleteAccountService.ts
@@ -5,7 +5,7 @@
 
 import { Inject, Injectable } from '@nestjs/common';
 import { Not, IsNull } from 'typeorm';
-import type { FollowingsRepository, MiUser, UsersRepository } from '@/models/_.js';
+import type { FollowingsRepository, MiMeta, MiUser, UsersRepository } from '@/models/_.js';
 import { QueueService } from '@/core/QueueService.js';
 import { DI } from '@/di-symbols.js';
 import { bindThis } from '@/decorators.js';
@@ -13,10 +13,14 @@ import { GlobalEventService } from '@/core/GlobalEventService.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { ApRendererService } from '@/core/activitypub/ApRendererService.js';
 import { ModerationLogService } from '@/core/ModerationLogService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 
 @Injectable()
 export class DeleteAccountService {
 	constructor(
+		@Inject(DI.meta)
+		private meta: MiMeta,
+
 		@Inject(DI.usersRepository)
 		private usersRepository: UsersRepository,
 
@@ -28,6 +32,7 @@ export class DeleteAccountService {
 		private queueService: QueueService,
 		private globalEventService: GlobalEventService,
 		private moderationLogService: ModerationLogService,
+		private systemAccountService: SystemAccountService,
 	) {
 	}
 
@@ -36,8 +41,13 @@ export class DeleteAccountService {
 		id: string;
 		host: string | null;
 	}, moderator?: MiUser): Promise<void> {
+		if (this.meta.rootUserId === user.id) throw new Error('cannot delete a root account');
+
 		const _user = await this.usersRepository.findOneByOrFail({ id: user.id });
-		if (_user.isRoot) throw new Error('cannot delete a root account');
+
+		if (user.host === null && _user.username.includes('.')) {
+			throw new Error('cannot delete a system account');
+		}
 
 		if (moderator != null) {
 			this.moderationLogService.log(moderator, 'deleteAccount', {
diff --git a/packages/backend/src/core/InstanceActorService.ts b/packages/backend/src/core/InstanceActorService.ts
deleted file mode 100644
index 22c47297a3..0000000000
--- a/packages/backend/src/core/InstanceActorService.ts
+++ /dev/null
@@ -1,57 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-import { Inject, Injectable } from '@nestjs/common';
-import { IsNull, Not } from 'typeorm';
-import type { MiLocalUser } from '@/models/User.js';
-import type { UsersRepository } from '@/models/_.js';
-import { MemorySingleCache } from '@/misc/cache.js';
-import { DI } from '@/di-symbols.js';
-import { CreateSystemUserService } from '@/core/CreateSystemUserService.js';
-import { bindThis } from '@/decorators.js';
-
-const ACTOR_USERNAME = 'instance.actor' as const;
-
-@Injectable()
-export class InstanceActorService {
-	private cache: MemorySingleCache<MiLocalUser>;
-
-	constructor(
-		@Inject(DI.usersRepository)
-		private usersRepository: UsersRepository,
-
-		private createSystemUserService: CreateSystemUserService,
-	) {
-		this.cache = new MemorySingleCache<MiLocalUser>(Infinity);
-	}
-
-	@bindThis
-	public async realLocalUsersPresent(): Promise<boolean> {
-		return await this.usersRepository.existsBy({
-			host: IsNull(),
-			username: Not(ACTOR_USERNAME),
-		});
-	}
-
-	@bindThis
-	public async getInstanceActor(): Promise<MiLocalUser> {
-		const cached = this.cache.get();
-		if (cached) return cached;
-
-		const user = await this.usersRepository.findOneBy({
-			host: IsNull(),
-			username: ACTOR_USERNAME,
-		}) as MiLocalUser | undefined;
-
-		if (user) {
-			this.cache.set(user);
-			return user;
-		} else {
-			const created = await this.createSystemUserService.createSystemUser(ACTOR_USERNAME) as MiLocalUser;
-			this.cache.set(created);
-			return created;
-		}
-	}
-}
diff --git a/packages/backend/src/core/MetaService.ts b/packages/backend/src/core/MetaService.ts
index 3d88d0aefe..40e7439f5f 100644
--- a/packages/backend/src/core/MetaService.ts
+++ b/packages/backend/src/core/MetaService.ts
@@ -53,7 +53,7 @@ export class MetaService implements OnApplicationShutdown {
 				case 'metaUpdated': {
 					this.cache = { // TODO: このあたりのデシリアライズ処理は各modelファイル内に関数としてexportしたい
 						...(body.after),
-						proxyAccount: null, // joinなカラムは通常取ってこないので
+						rootUser: null, // joinなカラムは通常取ってこないので
 					};
 					break;
 				}
@@ -113,17 +113,20 @@ export class MetaService implements OnApplicationShutdown {
 
 			if (before) {
 				await transactionalEntityManager.update(MiMeta, before.id, data);
-
-				const metas = await transactionalEntityManager.find(MiMeta, {
-					order: {
-						id: 'DESC',
-					},
-				});
-
-				return metas[0];
 			} else {
-				return await transactionalEntityManager.save(MiMeta, data);
+				await transactionalEntityManager.save(MiMeta, {
+					...data,
+					id: 'x',
+				});
 			}
+
+			const afters = await transactionalEntityManager.find(MiMeta, {
+				order: {
+					id: 'DESC',
+				},
+			});
+
+			return afters[0];
 		});
 
 		if (data.hiddenTags) {
diff --git a/packages/backend/src/core/ProxyAccountService.ts b/packages/backend/src/core/ProxyAccountService.ts
deleted file mode 100644
index c3ff2a68d3..0000000000
--- a/packages/backend/src/core/ProxyAccountService.ts
+++ /dev/null
@@ -1,28 +0,0 @@
-/*
- * SPDX-FileCopyrightText: syuilo and misskey-project
- * SPDX-License-Identifier: AGPL-3.0-only
- */
-
-import { Inject, Injectable } from '@nestjs/common';
-import type { MiMeta, UsersRepository } from '@/models/_.js';
-import type { MiLocalUser } from '@/models/User.js';
-import { DI } from '@/di-symbols.js';
-import { bindThis } from '@/decorators.js';
-
-@Injectable()
-export class ProxyAccountService {
-	constructor(
-		@Inject(DI.meta)
-		private meta: MiMeta,
-
-		@Inject(DI.usersRepository)
-		private usersRepository: UsersRepository,
-	) {
-	}
-
-	@bindThis
-	public async fetch(): Promise<MiLocalUser | null> {
-		if (this.meta.proxyAccountId == null) return null;
-		return await this.usersRepository.findOneByOrFail({ id: this.meta.proxyAccountId }) as MiLocalUser;
-	}
-}
diff --git a/packages/backend/src/core/RelayService.ts b/packages/backend/src/core/RelayService.ts
index db32114346..9120de1f9f 100644
--- a/packages/backend/src/core/RelayService.ts
+++ b/packages/backend/src/core/RelayService.ts
@@ -4,54 +4,35 @@
  */
 
 import { Inject, Injectable } from '@nestjs/common';
-import { IsNull } from 'typeorm';
-import type { MiLocalUser, MiUser } from '@/models/User.js';
-import type { RelaysRepository, UsersRepository } from '@/models/_.js';
+import type { MiUser } from '@/models/User.js';
+import type { RelaysRepository } from '@/models/_.js';
 import { IdService } from '@/core/IdService.js';
 import { MemorySingleCache } from '@/misc/cache.js';
 import type { MiRelay } from '@/models/Relay.js';
 import { QueueService } from '@/core/QueueService.js';
-import { CreateSystemUserService } from '@/core/CreateSystemUserService.js';
 import { ApRendererService } from '@/core/activitypub/ApRendererService.js';
 import { DI } from '@/di-symbols.js';
 import { deepClone } from '@/misc/clone.js';
 import { bindThis } from '@/decorators.js';
-
-const ACTOR_USERNAME = 'relay.actor' as const;
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 
 @Injectable()
 export class RelayService {
 	private relaysCache: MemorySingleCache<MiRelay[]>;
 
 	constructor(
-		@Inject(DI.usersRepository)
-		private usersRepository: UsersRepository,
-
 		@Inject(DI.relaysRepository)
 		private relaysRepository: RelaysRepository,
 
 		private idService: IdService,
 		private queueService: QueueService,
-		private createSystemUserService: CreateSystemUserService,
+		private systemAccountService: SystemAccountService,
 		private apRendererService: ApRendererService,
 	) {
 		this.relaysCache = new MemorySingleCache<MiRelay[]>(1000 * 60 * 10); // 10m
 	}
 
 	@bindThis
-	private async getRelayActor(): Promise<MiLocalUser> {
-		const user = await this.usersRepository.findOneBy({
-			host: IsNull(),
-			username: ACTOR_USERNAME,
-		});
-
-		if (user) return user as MiLocalUser;
-
-		const created = await this.createSystemUserService.createSystemUser(ACTOR_USERNAME);
-		return created as MiLocalUser;
-	}
-
-	@bindThis
 	public async addRelay(inbox: string): Promise<MiRelay> {
 		const relay = await this.relaysRepository.insertOne({
 			id: this.idService.gen(),
@@ -59,8 +40,8 @@ export class RelayService {
 			status: 'requesting',
 		});
 
-		const relayActor = await this.getRelayActor();
-		const follow = await this.apRendererService.renderFollowRelay(relay, relayActor);
+		const relayActor = await this.systemAccountService.fetch('relay');
+		const follow = this.apRendererService.renderFollowRelay(relay, relayActor);
 		const activity = this.apRendererService.addContext(follow);
 		this.queueService.deliver(relayActor, activity, relay.inbox, false);
 
@@ -77,7 +58,7 @@ export class RelayService {
 			throw new Error('relay not found');
 		}
 
-		const relayActor = await this.getRelayActor();
+		const relayActor = await this.systemAccountService.fetch('relay');
 		const follow = this.apRendererService.renderFollowRelay(relay, relayActor);
 		const undo = this.apRendererService.renderUndo(follow, relayActor);
 		const activity = this.apRendererService.addContext(undo);
diff --git a/packages/backend/src/core/RoleService.ts b/packages/backend/src/core/RoleService.ts
index 5af6b05942..01f3e0c116 100644
--- a/packages/backend/src/core/RoleService.ts
+++ b/packages/backend/src/core/RoleService.ts
@@ -101,7 +101,6 @@ export const DEFAULT_POLICIES: RolePolicies = {
 
 @Injectable()
 export class RoleService implements OnApplicationShutdown, OnModuleInit {
-	private rootUserIdCache: MemorySingleCache<MiUser['id']>;
 	private rolesCache: MemorySingleCache<MiRole[]>;
 	private roleAssignmentByUserIdCache: MemoryKVCache<MiRoleAssignment[]>;
 	private notificationService: NotificationService;
@@ -137,7 +136,6 @@ export class RoleService implements OnApplicationShutdown, OnModuleInit {
 		private moderationLogService: ModerationLogService,
 		private fanoutTimelineService: FanoutTimelineService,
 	) {
-		this.rootUserIdCache = new MemorySingleCache<MiUser['id']>(1000 * 60 * 60 * 24 * 7); // 1week. rootユーザのIDは不変なので長めに
 		this.rolesCache = new MemorySingleCache<MiRole[]>(1000 * 60 * 60); // 1h
 		this.roleAssignmentByUserIdCache = new MemoryKVCache<MiRoleAssignment[]>(1000 * 60 * 5); // 5m
 
@@ -406,15 +404,15 @@ export class RoleService implements OnApplicationShutdown, OnModuleInit {
 	}
 
 	@bindThis
-	public async isModerator(user: { id: MiUser['id']; isRoot: MiUser['isRoot'] } | null): Promise<boolean> {
+	public async isModerator(user: { id: MiUser['id'] } | null): Promise<boolean> {
 		if (user == null) return false;
-		return user.isRoot || (await this.getUserRoles(user.id)).some(r => r.isModerator || r.isAdministrator);
+		return (this.meta.rootUserId === user.id) || (await this.getUserRoles(user.id)).some(r => r.isModerator || r.isAdministrator);
 	}
 
 	@bindThis
-	public async isAdministrator(user: { id: MiUser['id']; isRoot: MiUser['isRoot'] } | null): Promise<boolean> {
+	public async isAdministrator(user: { id: MiUser['id'] } | null): Promise<boolean> {
 		if (user == null) return false;
-		return user.isRoot || (await this.getUserRoles(user.id)).some(r => r.isAdministrator);
+		return (this.meta.rootUserId === user.id) || (await this.getUserRoles(user.id)).some(r => r.isAdministrator);
 	}
 
 	@bindThis
@@ -463,16 +461,8 @@ export class RoleService implements OnApplicationShutdown, OnModuleInit {
 				.map(a => a.userId),
 		);
 
-		if (includeRoot) {
-			const rootUserId = await this.rootUserIdCache.fetch(async () => {
-				const it = await this.usersRepository.createQueryBuilder('users')
-					.select('id')
-					.where({ isRoot: true })
-					.getRawOne<{ id: string }>();
-				// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-				return it!.id;
-			});
-			resultSet.add(rootUserId);
+		if (includeRoot && this.meta.rootUserId) {
+			resultSet.add(this.meta.rootUserId);
 		}
 
 		return [...resultSet].sort((x, y) => x.localeCompare(y));
diff --git a/packages/backend/src/core/SignupService.ts b/packages/backend/src/core/SignupService.ts
index d2f09ea15d..5462cb0b13 100644
--- a/packages/backend/src/core/SignupService.ts
+++ b/packages/backend/src/core/SignupService.ts
@@ -16,11 +16,12 @@ import { MiUserKeypair } from '@/models/UserKeypair.js';
 import { MiUsedUsername } from '@/models/UsedUsername.js';
 import { generateNativeUserToken } from '@/misc/token.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
-import { InstanceActorService } from '@/core/InstanceActorService.js';
 import { bindThis } from '@/decorators.js';
 import UsersChart from '@/core/chart/charts/users.js';
 import { UtilityService } from '@/core/UtilityService.js';
 import { UserService } from '@/core/UserService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
+import { MetaService } from '@/core/MetaService.js';
 
 @Injectable()
 export class SignupService {
@@ -41,7 +42,8 @@ export class SignupService {
 		private userService: UserService,
 		private userEntityService: UserEntityService,
 		private idService: IdService,
-		private instanceActorService: InstanceActorService,
+		private systemAccountService: SystemAccountService,
+		private metaService: MetaService,
 		private usersChart: UsersChart,
 	) {
 	}
@@ -86,9 +88,7 @@ export class SignupService {
 			throw new Error('USED_USERNAME');
 		}
 
-		const isTheFirstUser = !await this.instanceActorService.realLocalUsersPresent();
-
-		if (!opts.ignorePreservedUsernames && !isTheFirstUser) {
+		if (!opts.ignorePreservedUsernames && this.meta.rootUserId != null) {
 			const isPreserved = this.meta.preservedUsernames.map(x => x.toLowerCase()).includes(username.toLowerCase());
 			if (isPreserved) {
 				throw new Error('USED_USERNAME');
@@ -129,7 +129,6 @@ export class SignupService {
 				usernameLower: username.toLowerCase(),
 				host: this.utilityService.toPunyNullable(host),
 				token: secret,
-				isRoot: isTheFirstUser,
 			}));
 
 			await transactionalEntityManager.save(new MiUserKeypair({
@@ -153,6 +152,10 @@ export class SignupService {
 		this.usersChart.update(account, true);
 		this.userService.notifySystemWebhook(account, 'userCreated');
 
+		if (this.meta.rootUserId == null) {
+			await this.metaService.update({ rootUserId: account.id });
+		}
+
 		return { account, secret };
 	}
 }
diff --git a/packages/backend/src/core/SystemAccountService.ts b/packages/backend/src/core/SystemAccountService.ts
new file mode 100644
index 0000000000..1e050c3054
--- /dev/null
+++ b/packages/backend/src/core/SystemAccountService.ts
@@ -0,0 +1,172 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { randomUUID } from 'node:crypto';
+import { Inject, Injectable } from '@nestjs/common';
+import { DataSource, IsNull } from 'typeorm';
+import bcrypt from 'bcryptjs';
+import { MiLocalUser, MiUser } from '@/models/User.js';
+import { MiSystemAccount, MiUsedUsername, MiUserKeypair, MiUserProfile, type UsersRepository, type SystemAccountsRepository } from '@/models/_.js';
+import type { MiMeta, UserProfilesRepository } from '@/models/_.js';
+import { MemoryKVCache } from '@/misc/cache.js';
+import { DI } from '@/di-symbols.js';
+import { bindThis } from '@/decorators.js';
+import { generateNativeUserToken } from '@/misc/token.js';
+import { IdService } from '@/core/IdService.js';
+import { genRsaKeyPair } from '@/misc/gen-key-pair.js';
+
+export const SYSTEM_ACCOUNT_TYPES = ['actor', 'relay', 'proxy'] as const;
+
+@Injectable()
+export class SystemAccountService {
+	private cache: MemoryKVCache<MiLocalUser>;
+
+	constructor(
+		@Inject(DI.db)
+		private db: DataSource,
+
+		@Inject(DI.meta)
+		private meta: MiMeta,
+
+		@Inject(DI.systemAccountsRepository)
+		private systemAccountsRepository: SystemAccountsRepository,
+
+		@Inject(DI.usersRepository)
+		private usersRepository: UsersRepository,
+
+		@Inject(DI.userProfilesRepository)
+		private userProfilesRepository: UserProfilesRepository,
+
+		private idService: IdService,
+	) {
+		this.cache = new MemoryKVCache<MiLocalUser>(1000 * 60 * 10); // 10m
+	}
+
+	@bindThis
+	public async list(): Promise<MiSystemAccount[]> {
+		const accounts = await this.systemAccountsRepository.findBy({});
+
+		return accounts;
+	}
+
+	@bindThis
+	public async fetch(type: typeof SYSTEM_ACCOUNT_TYPES[number]): Promise<MiLocalUser> {
+		const cached = this.cache.get(type);
+		if (cached) return cached;
+
+		const systemAccount = await this.systemAccountsRepository.findOne({
+			where: { type: type },
+			relations: ['user'],
+		});
+
+		if (systemAccount) {
+			this.cache.set(type, systemAccount.user as MiLocalUser);
+			return systemAccount.user as MiLocalUser;
+		} else {
+			const created = await this.createCorrespondingUser(type, {
+				username: `system.${type}`, // NOTE: (できれば避けたいが) . が含まれるかどうかでシステムアカウントかどうかを判定している処理もあるので変えないように
+				name: this.meta.name,
+			});
+			this.cache.set(type, created);
+			return created;
+		}
+	}
+
+	@bindThis
+	private async createCorrespondingUser(type: typeof SYSTEM_ACCOUNT_TYPES[number], extra: {
+		username: MiUser['username'];
+		name?: MiUser['name'];
+	}): Promise<MiLocalUser> {
+		const password = randomUUID();
+
+		// Generate hash of password
+		const salt = await bcrypt.genSalt(8);
+		const hash = await bcrypt.hash(password, salt);
+
+		// Generate secret
+		const secret = generateNativeUserToken();
+
+		const keyPair = await genRsaKeyPair();
+
+		let account!: MiUser;
+
+		// Start transaction
+		await this.db.transaction(async transactionalEntityManager => {
+			const exist = await transactionalEntityManager.findOneBy(MiUser, {
+				usernameLower: extra.username.toLowerCase(),
+				host: IsNull(),
+			});
+
+			if (exist) {
+				account = exist;
+				return;
+			}
+
+			account = await transactionalEntityManager.insert(MiUser, {
+				id: this.idService.gen(),
+				username: extra.username,
+				usernameLower: extra.username.toLowerCase(),
+				host: null,
+				token: secret,
+				isLocked: true,
+				isExplorable: false,
+				isBot: true,
+				name: extra.name,
+			}).then(x => transactionalEntityManager.findOneByOrFail(MiUser, x.identifiers[0]));
+
+			await transactionalEntityManager.insert(MiUserKeypair, {
+				publicKey: keyPair.publicKey,
+				privateKey: keyPair.privateKey,
+				userId: account.id,
+			});
+
+			await transactionalEntityManager.insert(MiUserProfile, {
+				userId: account.id,
+				autoAcceptFollowed: false,
+				password: hash,
+			});
+
+			await transactionalEntityManager.insert(MiUsedUsername, {
+				createdAt: new Date(),
+				username: extra.username.toLowerCase(),
+			});
+
+			await transactionalEntityManager.insert(MiSystemAccount, {
+				id: this.idService.gen(),
+				userId: account.id,
+				type: type,
+			});
+		});
+
+		return account as MiLocalUser;
+	}
+
+	@bindThis
+	public async updateCorrespondingUserProfile(type: typeof SYSTEM_ACCOUNT_TYPES[number], extra: {
+		name?: string;
+		description?: MiUserProfile['description'];
+	}): Promise<MiLocalUser> {
+		const user = await this.fetch(type);
+
+		const updates = {} as Partial<MiUser>;
+		if (extra.name !== undefined) updates.name = extra.name;
+
+		if (Object.keys(updates).length > 0) {
+			await this.usersRepository.update(user.id, updates);
+		}
+
+		const profileUpdates = {} as Partial<MiUserProfile>;
+		if (extra.description !== undefined) profileUpdates.description = extra.description;
+
+		if (Object.keys(profileUpdates).length > 0) {
+			await this.userProfilesRepository.update(user.id, profileUpdates);
+		}
+
+		const updated = await this.usersRepository.findOneByOrFail({ id: user.id }) as MiLocalUser;
+		this.cache.set(type, updated);
+
+		return updated;
+	}
+}
diff --git a/packages/backend/src/core/UserListService.ts b/packages/backend/src/core/UserListService.ts
index 6333356fe9..f0a8768c8f 100644
--- a/packages/backend/src/core/UserListService.ts
+++ b/packages/backend/src/core/UserListService.ts
@@ -15,11 +15,11 @@ import type { GlobalEvents } from '@/core/GlobalEventService.js';
 import { GlobalEventService } from '@/core/GlobalEventService.js';
 import { DI } from '@/di-symbols.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
-import { ProxyAccountService } from '@/core/ProxyAccountService.js';
 import { bindThis } from '@/decorators.js';
 import { QueueService } from '@/core/QueueService.js';
 import { RedisKVCache } from '@/misc/cache.js';
 import { RoleService } from '@/core/RoleService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 
 @Injectable()
 export class UserListService implements OnApplicationShutdown, OnModuleInit {
@@ -43,8 +43,8 @@ export class UserListService implements OnApplicationShutdown, OnModuleInit {
 		private userEntityService: UserEntityService,
 		private idService: IdService,
 		private globalEventService: GlobalEventService,
-		private proxyAccountService: ProxyAccountService,
 		private queueService: QueueService,
+		private systemAccountService: SystemAccountService,
 	) {
 		this.membersCache = new RedisKVCache<Set<string>>(this.redisClient, 'userListMembers', {
 			lifetime: 1000 * 60 * 30, // 30m
@@ -111,10 +111,8 @@ export class UserListService implements OnApplicationShutdown, OnModuleInit {
 
 		// このインスタンス内にこのリモートユーザーをフォローしているユーザーがいなくても投稿を受け取るためにダミーのユーザーがフォローしたということにする
 		if (this.userEntityService.isRemoteUser(target)) {
-			const proxy = await this.proxyAccountService.fetch();
-			if (proxy) {
-				this.queueService.createFollowJob([{ from: { id: proxy.id }, to: { id: target.id } }]);
-			}
+			const proxy = await this.systemAccountService.fetch('proxy');
+			this.queueService.createFollowJob([{ from: { id: proxy.id }, to: { id: target.id } }]);
 		}
 	}
 
diff --git a/packages/backend/src/core/WebhookTestService.ts b/packages/backend/src/core/WebhookTestService.ts
index 555a39f71c..f83dec67bf 100644
--- a/packages/backend/src/core/WebhookTestService.ts
+++ b/packages/backend/src/core/WebhookTestService.ts
@@ -73,7 +73,6 @@ function generateDummyUser(override?: Partial<MiUser>): MiUser {
 		isLocked: false,
 		isBot: false,
 		isCat: true,
-		isRoot: false,
 		isExplorable: true,
 		isHibernated: false,
 		isDeleted: false,
diff --git a/packages/backend/src/core/activitypub/ApRendererService.ts b/packages/backend/src/core/activitypub/ApRendererService.ts
index 8688015aff..83a095cdea 100644
--- a/packages/backend/src/core/activitypub/ApRendererService.ts
+++ b/packages/backend/src/core/activitypub/ApRendererService.ts
@@ -23,7 +23,7 @@ import { MfmService } from '@/core/MfmService.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { DriveFileEntityService } from '@/core/entities/DriveFileEntityService.js';
 import type { MiUserKeypair } from '@/models/UserKeypair.js';
-import type { UsersRepository, UserProfilesRepository, NotesRepository, DriveFilesRepository, PollsRepository } from '@/models/_.js';
+import type { UsersRepository, UserProfilesRepository, NotesRepository, DriveFilesRepository, PollsRepository, MiMeta } from '@/models/_.js';
 import { bindThis } from '@/decorators.js';
 import { CustomEmojiService } from '@/core/CustomEmojiService.js';
 import { IdService } from '@/core/IdService.js';
@@ -39,6 +39,9 @@ export class ApRendererService {
 		@Inject(DI.config)
 		private config: Config,
 
+		@Inject(DI.meta)
+		private meta: MiMeta,
+
 		@Inject(DI.usersRepository)
 		private usersRepository: UsersRepository,
 
@@ -186,7 +189,7 @@ export class ApRendererService {
 				url: emoji.publicUrl || emoji.originalUrl,
 			},
 			_misskey_license: {
-				freeText: emoji.license
+				freeText: emoji.license,
 			},
 		};
 	}
@@ -256,6 +259,38 @@ export class ApRendererService {
 	}
 
 	@bindThis
+	public renderIdenticon(user: MiLocalUser): IApImage {
+		return {
+			type: 'Image',
+			url: this.userEntityService.getIdenticonUrl(user),
+			sensitive: false,
+			name: null,
+		};
+	}
+
+	@bindThis
+	public renderSystemAvatar(user: MiLocalUser): IApImage {
+		if (this.meta.iconUrl == null) return this.renderIdenticon(user);
+		return {
+			type: 'Image',
+			url: this.meta.iconUrl,
+			sensitive: false,
+			name: null,
+		};
+	}
+
+	@bindThis
+	public renderSystemBanner(): IApImage | null {
+		if (this.meta.bannerUrl == null) return null;
+		return {
+			type: 'Image',
+			url: this.meta.bannerUrl,
+			sensitive: false,
+			name: null,
+		};
+	}
+
+	@bindThis
 	public renderKey(user: MiLocalUser, key: MiUserKeypair, postfix?: string): IKey {
 		return {
 			id: `${this.config.url}/users/${user.id}${postfix ?? '/publickey'}`,
@@ -503,8 +538,8 @@ export class ApRendererService {
 			_misskey_requireSigninToViewContents: user.requireSigninToViewContents,
 			_misskey_makeNotesFollowersOnlyBefore: user.makeNotesFollowersOnlyBefore,
 			_misskey_makeNotesHiddenBefore: user.makeNotesHiddenBefore,
-			icon: avatar ? this.renderImage(avatar) : null,
-			image: banner ? this.renderImage(banner) : null,
+			icon: avatar ? this.renderImage(avatar) : isSystem ? this.renderSystemAvatar(user) : this.renderIdenticon(user),
+			image: banner ? this.renderImage(banner) : isSystem ? this.renderSystemBanner() : null,
 			tag,
 			manuallyApprovesFollowers: user.isLocked,
 			discoverable: user.isExplorable,
diff --git a/packages/backend/src/core/activitypub/ApResolverService.ts b/packages/backend/src/core/activitypub/ApResolverService.ts
index fb963294cb..2534899ad1 100644
--- a/packages/backend/src/core/activitypub/ApResolverService.ts
+++ b/packages/backend/src/core/activitypub/ApResolverService.ts
@@ -6,7 +6,6 @@
 import { Inject, Injectable } from '@nestjs/common';
 import { IsNull, Not } from 'typeorm';
 import type { MiLocalUser, MiRemoteUser } from '@/models/User.js';
-import { InstanceActorService } from '@/core/InstanceActorService.js';
 import type { NotesRepository, PollsRepository, NoteReactionsRepository, UsersRepository, FollowRequestsRepository, MiMeta } from '@/models/_.js';
 import type { Config } from '@/config.js';
 import { HttpRequestService } from '@/core/HttpRequestService.js';
@@ -15,13 +14,14 @@ import { UtilityService } from '@/core/UtilityService.js';
 import { bindThis } from '@/decorators.js';
 import { LoggerService } from '@/core/LoggerService.js';
 import type Logger from '@/logger.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
+import { IdentifiableError } from '@/misc/identifiable-error.js';
 import { isCollectionOrOrderedCollection } from './type.js';
 import { ApDbResolverService } from './ApDbResolverService.js';
 import { ApRendererService } from './ApRendererService.js';
 import { ApRequestService } from './ApRequestService.js';
-import type { IObject, ICollection, IOrderedCollection } from './type.js';
-import { IdentifiableError } from '@/misc/identifiable-error.js';
 import { FetchAllowSoftFailMask } from './misc/check-against-url.js';
+import type { IObject, ICollection, IOrderedCollection } from './type.js';
 
 export class Resolver {
 	private history: Set<string>;
@@ -37,7 +37,7 @@ export class Resolver {
 		private noteReactionsRepository: NoteReactionsRepository,
 		private followRequestsRepository: FollowRequestsRepository,
 		private utilityService: UtilityService,
-		private instanceActorService: InstanceActorService,
+		private systemAccountService: SystemAccountService,
 		private apRequestService: ApRequestService,
 		private httpRequestService: HttpRequestService,
 		private apRendererService: ApRendererService,
@@ -105,7 +105,7 @@ export class Resolver {
 		}
 
 		if (this.config.signToActivityPubGet && !this.user) {
-			this.user = await this.instanceActorService.getInstanceActor();
+			this.user = await this.systemAccountService.fetch('actor');
 		}
 
 		const object = (this.user
@@ -119,7 +119,7 @@ export class Resolver {
 		) {
 			throw new IdentifiableError('72180409-793c-4973-868e-5a118eb5519b', 'invalid response');
 		}
-		
+
 		return object;
 	}
 
@@ -202,7 +202,7 @@ export class ApResolverService {
 		private followRequestsRepository: FollowRequestsRepository,
 
 		private utilityService: UtilityService,
-		private instanceActorService: InstanceActorService,
+		private systemAccountService: SystemAccountService,
 		private apRequestService: ApRequestService,
 		private httpRequestService: HttpRequestService,
 		private apRendererService: ApRendererService,
@@ -222,7 +222,7 @@ export class ApResolverService {
 			this.noteReactionsRepository,
 			this.followRequestsRepository,
 			this.utilityService,
-			this.instanceActorService,
+			this.systemAccountService,
 			this.apRequestService,
 			this.httpRequestService,
 			this.apRendererService,
diff --git a/packages/backend/src/core/entities/MetaEntityService.ts b/packages/backend/src/core/entities/MetaEntityService.ts
index 7ad6071ceb..08717bd066 100644
--- a/packages/backend/src/core/entities/MetaEntityService.ts
+++ b/packages/backend/src/core/entities/MetaEntityService.ts
@@ -11,8 +11,7 @@ import type { MiMeta } from '@/models/Meta.js';
 import type { AdsRepository } from '@/models/_.js';
 import { MAX_NOTE_TEXT_LENGTH } from '@/const.js';
 import { bindThis } from '@/decorators.js';
-import { UserEntityService } from '@/core/entities/UserEntityService.js';
-import { InstanceActorService } from '@/core/InstanceActorService.js';
+import { SystemAccountService } from '@/core/SystemAccountService.js';
 import type { Config } from '@/config.js';
 import { DI } from '@/di-symbols.js';
 import { DEFAULT_POLICIES } from '@/core/RoleService.js';
@@ -29,8 +28,7 @@ export class MetaEntityService {
 		@Inject(DI.adsRepository)
 		private adsRepository: AdsRepository,
 
-		private userEntityService: UserEntityService,
-		private instanceActorService: InstanceActorService,
+		private systemAccountService: SystemAccountService,
 	) { }
 
 	@bindThis
@@ -149,14 +147,14 @@ export class MetaEntityService {
 
 		const packed = await this.pack(instance);
 
-		const proxyAccount = instance.proxyAccountId ? await this.userEntityService.pack(instance.proxyAccountId).catch(() => null) : null;
+		const proxyAccount = await this.systemAccountService.fetch('proxy');
 
 		const packDetailed: Packed<'MetaDetailed'> = {
 			...packed,
 			cacheRemoteFiles: instance.cacheRemoteFiles,
 			cacheRemoteSensitiveFiles: instance.cacheRemoteSensitiveFiles,
-			requireSetup: !await this.instanceActorService.realLocalUsersPresent(),
-			proxyAccountName: proxyAccount ? proxyAccount.username : null,
+			requireSetup: this.meta.rootUserId == null,
+			proxyAccountName: proxyAccount.username,
 			features: {
 				localTimeline: instance.policies.ltlAvailable,
 				globalTimeline: instance.policies.gtlAvailable,
diff --git a/packages/backend/src/core/entities/UserEntityService.ts b/packages/backend/src/core/entities/UserEntityService.ts
index fbd3892dd4..69f698d9cb 100644
--- a/packages/backend/src/core/entities/UserEntityService.ts
+++ b/packages/backend/src/core/entities/UserEntityService.ts
@@ -28,6 +28,7 @@ import type {
 	FollowingsRepository,
 	FollowRequestsRepository,
 	MiFollowing,
+	MiMeta,
 	MiUserNotePining,
 	MiUserProfile,
 	MutingsRepository,
@@ -100,6 +101,9 @@ export class UserEntityService implements OnModuleInit {
 		@Inject(DI.config)
 		private config: Config,
 
+		@Inject(DI.meta)
+		private meta: MiMeta,
+
 		@Inject(DI.redis)
 		private redisClient: Redis.Redis,
 
@@ -381,7 +385,11 @@ export class UserEntityService implements OnModuleInit {
 
 	@bindThis
 	public getIdenticonUrl(user: MiUser): string {
-		return `${this.config.url}/identicon/${user.username.toLowerCase()}@${user.host ?? this.config.host}`;
+		if ((user.host == null || user.host === this.config.host) && user.username.includes('.') && this.meta.iconUrl) { // ローカルのシステムアカウントの場合
+			return this.meta.iconUrl;
+		} else {
+			return `${this.config.url}/identicon/${user.username.toLowerCase()}@${user.host ?? this.config.host}`;
+		}
 	}
 
 	@bindThis