diff --git a/packages/backend/src/core/CacheService.ts b/packages/backend/src/core/CacheService.ts
index 78bb4f70e98b909af215e46b0e85ce3e82bc2635..68f37d0cf9df731634126d37a795da74349740a3 100644
--- a/packages/backend/src/core/CacheService.ts
+++ b/packages/backend/src/core/CacheService.ts
@@ -16,10 +16,10 @@ import type { OnApplicationShutdown } from '@nestjs/common';
 
 @Injectable()
 export class CacheService implements OnApplicationShutdown {
-	public userByIdCache: MemoryKVCache<MiUser, MiUser | string>;
-	public localUserByNativeTokenCache: MemoryKVCache<MiLocalUser | null, string | null>;
+	public userByIdCache: MemoryKVCache<MiUser>;
+	public localUserByNativeTokenCache: MemoryKVCache<MiLocalUser | null>;
 	public localUserByIdCache: MemoryKVCache<MiLocalUser>;
-	public uriPersonCache: MemoryKVCache<MiUser | null, string | null>;
+	public uriPersonCache: MemoryKVCache<MiUser | null>;
 	public userProfileCache: RedisKVCache<MiUserProfile>;
 	public userMutingsCache: RedisKVCache<Set<string>>;
 	public userBlockingCache: RedisKVCache<Set<string>>;
@@ -56,42 +56,10 @@ export class CacheService implements OnApplicationShutdown {
 	) {
 		//this.onMessage = this.onMessage.bind(this);
 
-		const localUserByIdCache = new MemoryKVCache<MiLocalUser>(1000 * 60 * 60 * 6 /* 6h */);
-		this.localUserByIdCache	= localUserByIdCache;
-
-		// ローカルユーザーならlocalUserByIdCacheにデータを追加し、こちらにはid(文字列)だけを追加する
-		const userByIdCache = new MemoryKVCache<MiUser, MiUser | string>(1000 * 60 * 60 * 6 /* 6h */, {
-			toMapConverter: user => {
-				if (user.host === null) {
-					localUserByIdCache.set(user.id, user as MiLocalUser);
-					return user.id;
-				}
-
-				return user;
-			},
-			fromMapConverter: userOrId => typeof userOrId === 'string' ? localUserByIdCache.get(userOrId) : userOrId,
-		});
-		this.userByIdCache = userByIdCache;
-
-		this.localUserByNativeTokenCache = new MemoryKVCache<MiLocalUser | null, string | null>(Infinity, {
-			toMapConverter: user => {
-				if (user === null) return null;
-
-				localUserByIdCache.set(user.id, user);
-				return user.id;
-			},
-			fromMapConverter: id => id === null ? null : localUserByIdCache.get(id),
-		});
-		this.uriPersonCache = new MemoryKVCache<MiUser | null, string | null>(Infinity, {
-			toMapConverter: user => {
-				if (user === null) return null;
-				if (user.isDeleted) return null;
-
-				userByIdCache.set(user.id, user);
-				return user.id;
-			},
-			fromMapConverter: id => id === null ? null : userByIdCache.get(id),
-		});
+		this.userByIdCache = new MemoryKVCache<MiUser>(Infinity);
+		this.localUserByNativeTokenCache = new MemoryKVCache<MiLocalUser | null>(Infinity);
+		this.localUserByIdCache = new MemoryKVCache<MiLocalUser>(Infinity);
+		this.uriPersonCache = new MemoryKVCache<MiUser | null>(Infinity);
 
 		this.userProfileCache = new RedisKVCache<MiUserProfile>(this.redisClient, 'userProfile', {
 			lifetime: 1000 * 60 * 30, // 30m
diff --git a/packages/backend/src/misc/cache.ts b/packages/backend/src/misc/cache.ts
index e0f7ea6ed9ab67ccc6fcea388c2a7f155e0f03a9..4cde6e12d38e60a890887af32a14b7c7c9753482 100644
--- a/packages/backend/src/misc/cache.ts
+++ b/packages/backend/src/misc/cache.ts
@@ -186,28 +186,14 @@ export class RedisSingleCache<T> {
 
 // TODO: メモリ節約のためあまり参照されないキーを定期的に削除できるようにする？
 
-function nothingToDo<T, V = T>(value: T): V {
-	return value as unknown as V;
-}
-
-export class MemoryKVCache<T, V = T> {
-	public cache: Map<string, { date: number; value: V; }>;
+export class MemoryKVCache<T> {
+	public cache: Map<string, { date: number; value: T; }>;
 	private lifetime: number;
-	private gcIntervalHandle: NodeJS.Timeout;
-	private toMapConverter: (value: T) => V;
-	private fromMapConverter: (cached: V) => T | undefined;
-
-	constructor(lifetime: MemoryKVCache<never>['lifetime'], options: {
-		toMapConverter: (value: T) => V;
-		fromMapConverter: (cached: V) => T | undefined;
-	} = {
-		toMapConverter: nothingToDo,
-		fromMapConverter: nothingToDo,
-	}) {
+	private gcIntervalHandle: NodeJS.Timer;
+
+	constructor(lifetime: MemoryKVCache<never>['lifetime']) {
 		this.cache = new Map();
 		this.lifetime = lifetime;
-		this.toMapConverter = options.toMapConverter;
-		this.fromMapConverter = options.fromMapConverter;
 
 		this.gcIntervalHandle = setInterval(() => {
 			this.gc();
@@ -218,7 +204,7 @@ export class MemoryKVCache<T, V = T> {
 	public set(key: string, value: T): void {
 		this.cache.set(key, {
 			date: Date.now(),
-			value: this.toMapConverter(value),
+			value,
 		});
 	}
 
@@ -230,7 +216,7 @@ export class MemoryKVCache<T, V = T> {
 			this.cache.delete(key);
 			return undefined;
 		}
-		return this.fromMapConverter(cached.value);
+		return cached.value;
 	}
 
 	@bindThis
@@ -241,10 +227,9 @@ export class MemoryKVCache<T, V = T> {
 	/**
 	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
 	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
-	 * fetcherの引数はcacheに保存されている値があれば渡されます
 	 */
 	@bindThis
-	public async fetch(key: string, fetcher: (value: V | undefined) => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
+	public async fetch(key: string, fetcher: () => Promise<T>, validator?: (cachedValue: T) => boolean): Promise<T> {
 		const cachedValue = this.get(key);
 		if (cachedValue !== undefined) {
 			if (validator) {
@@ -259,7 +244,7 @@ export class MemoryKVCache<T, V = T> {
 		}
 
 		// Cache MISS
-		const value = await fetcher(this.cache.get(key)?.value);
+		const value = await fetcher();
 		this.set(key, value);
 		return value;
 	}
@@ -267,10 +252,9 @@ export class MemoryKVCache<T, V = T> {
 	/**
 	 * キャッシュがあればそれを返し、無ければfetcherを呼び出して結果をキャッシュ&返します
 	 * optional: キャッシュが存在してもvalidatorでfalseを返すとキャッシュ無効扱いにします
-	 * fetcherの引数はcacheに保存されている値があれば渡されます
 	 */
 	@bindThis
-	public async fetchMaybe(key: string, fetcher: (value: V | undefined) => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
+	public async fetchMaybe(key: string, fetcher: () => Promise<T | undefined>, validator?: (cachedValue: T) => boolean): Promise<T | undefined> {
 		const cachedValue = this.get(key);
 		if (cachedValue !== undefined) {
 			if (validator) {
@@ -285,7 +269,7 @@ export class MemoryKVCache<T, V = T> {
 		}
 
 		// Cache MISS
-		const value = await fetcher(this.cache.get(key)?.value);
+		const value = await fetcher();
 		if (value !== undefined) {
 			this.set(key, value);
 		}