diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a12c964..86bcd1c 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,5 +1,11 @@
 # CONTRIBUTING
 
+Misskey Tools へのコントリビューションにご関心いただき、誠にありがとうございます。
+
+このドキュメントでは、本プロジェクトの開発方針をまとめています。IssueやPull Requestの作成前に、必ずご一読ください。
+
+なお、開発の進行に応じて、ドキュメントの内容は大きく変わることがあります。
+
 ## データベース スキーマの編集
 
 * TypeScriptのコーディング規約に一致するように、命名規則を定める
@@ -10,4 +16,10 @@
   * `//` （/2つ）だと整形時に削除されてしまうため注意
 * schema.prisma を編集したら、次のコマンドを実行してSQLファイルを生成する
   * `prisma migrate dev --name 変更名`
-  * 変更名は snake_case
\ No newline at end of file
+  * 変更名は snake_case
+
+## tRPCでのデータ返却時はDTOを渡すこと
+
+意図しないデータの漏洩を防ぐため、フロントエンドへデータを渡す場合は、必ずDBの実データではなく、DTOへの変換を通してください。
+
+また、実データを返すと、tRPCの型定義にPrismaの型が含まれてしまい、フロントエンド側からTypeScriptのエラー TS2742 が発生します。
diff --git a/packages/backend/src/server/api/dto/account.ts b/packages/backend/src/server/api/dto/account.ts
new file mode 100644
index 0000000..c237500
--- /dev/null
+++ b/packages/backend/src/server/api/dto/account.ts
@@ -0,0 +1,17 @@
+import { Account } from '@prisma/client';
+import { z } from 'zod';
+
+
+export const accountDtoSchema = z.object({
+  id: z.string(),
+  name: z.string(),
+  isAdmin: z.boolean(),
+}).strict();
+
+export type AccountDto = z.infer<typeof accountDtoSchema>;
+
+export const toAccountDto = (a: Account): AccountDto => ({
+  id: a.id,
+  name: a.name,
+  isAdmin: a.isAdmin,
+});
diff --git a/packages/backend/src/server/api/dto/meta.ts b/packages/backend/src/server/api/dto/meta.ts
new file mode 100644
index 0000000..66ce50d
--- /dev/null
+++ b/packages/backend/src/server/api/dto/meta.ts
@@ -0,0 +1,9 @@
+import { currentTokenVersion } from 'tools-shared/dist/const';
+import { z } from 'zod';
+
+export const metaDtoSchema = z.object({
+  version: z.string(),
+  currentTokenVersion: z.literal(currentTokenVersion),
+}).strict();
+
+export type MetaDto = z.infer<typeof metaDtoSchema>;
diff --git a/packages/backend/src/server/api/dto/misskey-session.ts b/packages/backend/src/server/api/dto/misskey-session.ts
new file mode 100644
index 0000000..d6ae6f1
--- /dev/null
+++ b/packages/backend/src/server/api/dto/misskey-session.ts
@@ -0,0 +1,16 @@
+import { MisskeySession } from '@prisma/client';
+import { z } from 'zod';
+
+export const misskeySessionDtoSchema = z.object({
+  id: z.string(),
+  username: z.string(),
+  host: z.string(),
+}).strict();
+
+export type MisskeySessionDto = z.infer<typeof misskeySessionDtoSchema>;
+
+export const toMisskeySessionDto = (s: MisskeySession): MisskeySessionDto => ({
+  id: s.id,
+  username: s.username,
+  host: s.host,
+});
diff --git a/packages/backend/src/server/api/procedures/session.ts b/packages/backend/src/server/api/procedures/session.ts
index 4fd34eb..ddba310 100644
--- a/packages/backend/src/server/api/procedures/session.ts
+++ b/packages/backend/src/server/api/procedures/session.ts
@@ -3,13 +3,14 @@ import { TRPCError } from '@trpc/server';
 import { middleware, procedure } from '@/server/api/trpc.js';
 
 const hasSession = middleware(({ next, ctx }) => {
-  if (!ctx.account) {
+  const { account } = ctx;
+  if (!account) {
     throw new TRPCError({ code: 'UNAUTHORIZED' });
   }
   return next({
     ctx: {
       token: ctx.token,
-      user: ctx.account,
+      account: account,
     },
   });
 });
diff --git a/packages/backend/src/server/api/routers/account.ts b/packages/backend/src/server/api/routers/account.ts
index 43945cc..1b5ad44 100644
--- a/packages/backend/src/server/api/routers/account.ts
+++ b/packages/backend/src/server/api/routers/account.ts
@@ -1,17 +1,31 @@
-import { TRPCError } from '@trpc/server';
+
 import { z } from 'zod';
 
+import { accountDtoSchema, toAccountDto } from '../dto/account';
+import { misskeySessionDtoSchema } from '../dto/misskey-session';
+
+import { prisma } from '@/libs/prisma';
 import { sessionProcedure } from '@/server/api/procedures/session.js';
-import { procedure, router } from '@/server/api/trpc.js';
-import { getAccountByAccessToken } from '@/services/accounts/get-account-by-access-token.js';
+import { router } from '@/server/api/trpc.js';
+
 
 export const accountRouter = router({
-  get: sessionProcedure.query(({ ctx }) => ctx.user),
-  getByToken: procedure.input(z.string()).query(async ({ input: token }) => {
-    const account = await getAccountByAccessToken(token);
-    if (!account) {
-      throw new TRPCError({ code: 'NOT_FOUND' });
-    }
-    return account;
-  }),
+  getMyself: sessionProcedure
+    .output(accountDtoSchema)
+    .query(({ ctx }) => {
+      return toAccountDto(ctx.account);
+    }),
+  getMisskeySessions: sessionProcedure
+    .output(z.array(misskeySessionDtoSchema))
+    .query(async ({ ctx }) => {
+      const sessions = await prisma.misskeySession.findMany({
+        where: { accountId: ctx.account.id },
+        select: {
+          id: true,
+          username: true,
+          host: true,
+        },
+      });
+      return sessions;
+    }),
 });
diff --git a/packages/backend/src/server/api/routers/meta.ts b/packages/backend/src/server/api/routers/meta.ts
index 73e172b..99297fd 100644
--- a/packages/backend/src/server/api/routers/meta.ts
+++ b/packages/backend/src/server/api/routers/meta.ts
@@ -1,12 +1,15 @@
 import { currentTokenVersion } from 'tools-shared/dist/const.js';
 
+import { metaDtoSchema } from '../dto/meta';
+
 import { meta } from '@/config';
 import { procedure, router } from '@/server/api/trpc';
 
-
 export const metaRouter = router({
-  get: procedure.query(() => ({
-    version: meta.version,
-    currentTokenVersion,
-  })),
+  get: procedure
+    .output(metaDtoSchema)
+    .query(() => ({
+      version: meta.version,
+      currentTokenVersion,
+    })),
 });
diff --git a/packages/backend/src/services/sessions/process-login.ts b/packages/backend/src/services/sessions/process-login.ts
index 56999f0..2022fff 100644
--- a/packages/backend/src/services/sessions/process-login.ts
+++ b/packages/backend/src/services/sessions/process-login.ts
@@ -29,7 +29,7 @@ export const processLogin = async (misskeyUser: MkUser, host: string, misskeyTok
         },
       },
       // Note: 少しでもデータ転送量を抑える（Prismaはcreateの後に絶対selectを実行してしまう）
-      select: {},
+      select: { id: true },
     });
     return accessToken;
   }