diff --git a/src/idz/decoder/index.ts b/src/idz/decoder/index.ts
index afaabe1..63ff947 100644
--- a/src/idz/decoder/index.ts
+++ b/src/idz/decoder/index.ts
@@ -36,6 +36,7 @@ import { saveTimeAttack1, saveTimeAttack2 } from "./saveTimeAttack";
 import { saveTopic } from "./saveTopic";
 import { unlockProfile } from "./unlockProfile";
 import { updateProvisionalStoreRank } from "./updateProvisionalStoreRank";
+import { updateTeamLeader } from "./updateTeamLeader";
 import { updateTeamMember } from "./updateTeamMember";
 import {
   updateStoryClearNum1,
@@ -101,6 +102,7 @@ const funcList: ReaderFn[] = [
   updateResult,
   updateStoryClearNum1,
   updateStoryClearNum2,
+  updateTeamLeader,
   updateTeamMember,
   updateTeamPoints,
   updateUiReport,
diff --git a/src/idz/decoder/updateTeamLeader.ts b/src/idz/decoder/updateTeamLeader.ts
new file mode 100644
index 0000000..ca247b4
--- /dev/null
+++ b/src/idz/decoder/updateTeamLeader.ts
@@ -0,0 +1,17 @@
+import { RequestCode } from "./_defs";
+import { ExtId } from "../model/base";
+import { Team } from "../model/team";
+import { UpdateTeamLeaderRequest } from "../request/updateTeamLeader";
+import { AimeId } from "../../model";
+
+updateTeamLeader.msgCode = 0x008a as RequestCode;
+updateTeamLeader.msgLen = 0x0020;
+
+export function updateTeamLeader(buf: Buffer): UpdateTeamLeaderRequest {
+  return {
+    type: "update_team_leader_req",
+    aimeId: buf.readUInt32LE(0x0004) as AimeId,
+    teamExtId: buf.readUInt32LE(0x0008) as ExtId<Team>,
+    field_000C: buf.slice(0x000c, buf.indexOf("\0", 0x000c)).toString("ascii"),
+  };
+}
diff --git a/src/idz/encoder/index.ts b/src/idz/encoder/index.ts
index 6dbe659..f6a3386 100644
--- a/src/idz/encoder/index.ts
+++ b/src/idz/encoder/index.ts
@@ -29,6 +29,7 @@ import { saveTopic } from "./saveTopic";
 import { unlockProfile } from "./unlockProfile";
 import { updateProvisionalStoreRank } from "./updateProvisionalStoreRank";
 import { updateStoryClearNum } from "./updateStoryClearNum";
+import { updateTeamLeader } from "./updateTeamLeader";
 import { updateTeamMember } from "./updateTeamMember";
 import { Response } from "../response";
 
@@ -121,6 +122,9 @@ function encode(res: Response): Buffer {
     case "update_story_clear_num_res":
       return updateStoryClearNum(res);
 
+    case "update_team_leader_res":
+      return updateTeamLeader(res);
+
     case "update_team_member_res":
       return updateTeamMember(res);
 
diff --git a/src/idz/encoder/updateTeamLeader.ts b/src/idz/encoder/updateTeamLeader.ts
new file mode 100644
index 0000000..b0c7ccc
--- /dev/null
+++ b/src/idz/encoder/updateTeamLeader.ts
@@ -0,0 +1,10 @@
+import { UpdateTeamLeaderResponse } from "../response/updateTeamLeader";
+
+export function updateTeamLeader(res: UpdateTeamLeaderResponse): Buffer {
+  const buf = Buffer.alloc(0x0010);
+
+  buf.writeUInt16LE(0x008b, 0x0000);
+  buf.writeUInt32LE(res.status, 0x0004);
+
+  return buf;
+}
diff --git a/src/idz/handler/index.ts b/src/idz/handler/index.ts
index 130e49a..68224b9 100644
--- a/src/idz/handler/index.ts
+++ b/src/idz/handler/index.ts
@@ -35,6 +35,7 @@ import { unlockProfile } from "./unlockProfile";
 import { updateProvisionalStoreRank } from "./updateProvisionalStoreRank";
 import { updateResult } from "./updateResult";
 import { updateStoryClearNum } from "./updateStoryClearNum";
+import { updateTeamLeader } from "./updateTeamLeader";
 import { updateTeamMember } from "./updateTeamMember";
 import { updateTeamPoints } from "./updateTeamPoints";
 import { updateUiReport } from "./updateUiReport";
@@ -159,6 +160,9 @@ export async function dispatch(
     case "update_story_clear_num_req":
       return updateStoryClearNum(w, req);
 
+    case "update_team_leader_req":
+      return updateTeamLeader(w, req);
+
     case "update_team_member_req":
       return updateTeamMember(w, req);
 
diff --git a/src/idz/handler/updateTeamLeader.ts b/src/idz/handler/updateTeamLeader.ts
new file mode 100644
index 0000000..4ac1d89
--- /dev/null
+++ b/src/idz/handler/updateTeamLeader.ts
@@ -0,0 +1,18 @@
+import { UpdateTeamLeaderRequest } from "../request/updateTeamLeader";
+import { UpdateTeamLeaderResponse } from "../response/updateTeamLeader";
+import { Repositories } from "../repo";
+
+export async function updateTeamLeader(
+  w: Repositories,
+  req: UpdateTeamLeaderRequest
+): Promise<UpdateTeamLeaderResponse> {
+  const profileId = await w.profile().find(req.aimeId);
+  const teamId = await w.teams().find(req.teamExtId);
+
+  await w.teamMembers().makeLeader(teamId, profileId);
+
+  return {
+    type: "update_team_leader_res",
+    status: 0,
+  };
+}
diff --git a/src/idz/request/index.ts b/src/idz/request/index.ts
index 8b5aef2..92265d1 100644
--- a/src/idz/request/index.ts
+++ b/src/idz/request/index.ts
@@ -35,6 +35,7 @@ import { UnlockProfileRequest } from "./unlockProfile";
 import { UpdateProvisionalStoreRankRequest } from "./updateProvisionalStoreRank";
 import { UpdateResultRequest } from "./updateResult";
 import { UpdateStoryClearNumRequest } from "./updateStoryClearNum";
+import { UpdateTeamLeaderRequest } from "./updateTeamLeader";
 import { UpdateTeamMemberRequest } from "./updateTeamMember";
 import { UpdateTeamPointsRequest } from "./updateTeamPoints";
 import { UpdateUiReportRequest } from "./updateUiReport";
@@ -78,6 +79,7 @@ export type Request =
   | UpdateProvisionalStoreRankRequest
   | UpdateResultRequest
   | UpdateStoryClearNumRequest
+  | UpdateTeamLeaderRequest
   | UpdateTeamMemberRequest
   | UpdateTeamPointsRequest
   | UpdateUiReportRequest
diff --git a/src/idz/request/updateTeamLeader.ts b/src/idz/request/updateTeamLeader.ts
new file mode 100644
index 0000000..741b402
--- /dev/null
+++ b/src/idz/request/updateTeamLeader.ts
@@ -0,0 +1,10 @@
+import { ExtId } from "../model/base";
+import { Team } from "../model/team";
+import { AimeId } from "../../model";
+
+export interface UpdateTeamLeaderRequest {
+  type: "update_team_leader_req";
+  aimeId: AimeId;
+  teamExtId: ExtId<Team>;
+  field_000C: string;
+}
diff --git a/src/idz/response/index.ts b/src/idz/response/index.ts
index edaad65..44ebfcd 100644
--- a/src/idz/response/index.ts
+++ b/src/idz/response/index.ts
@@ -27,6 +27,7 @@ import { SaveTimeAttackResponse } from "./saveTimeAttack";
 import { SaveTopicResponse } from "./saveTopic";
 import { UpdateProvisionalStoreRankResponse } from "./updateProvisionalStoreRank";
 import { UpdateStoryClearNumResponse } from "./updateStoryClearNum";
+import { UpdateTeamLeaderResponse } from "./updateTeamLeader";
 import { UpdateTeamMemberResponse } from "./updateTeamMember";
 import { UnlockProfileResponse } from "./unlockProfile";
 
@@ -56,6 +57,7 @@ export type Response =
   | UnlockProfileResponse
   | UpdateProvisionalStoreRankResponse
   | UpdateStoryClearNumResponse
+  | UpdateTeamLeaderResponse
   | UpdateTeamMemberResponse
   | SaveExpeditionResponse
   | SaveGarageResponse
diff --git a/src/idz/response/updateTeamLeader.ts b/src/idz/response/updateTeamLeader.ts
new file mode 100644
index 0000000..5fdfbdc
--- /dev/null
+++ b/src/idz/response/updateTeamLeader.ts
@@ -0,0 +1,4 @@
+export interface UpdateTeamLeaderResponse {
+  type: "update_team_leader_res";
+  status: number;
+}