diff --git a/lefthook.yml b/lefthook.yml
index 85dc788..4477b36 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -1,5 +1,5 @@
 pre-commit:
   commands:
-    check:
-      glob: "*.{js,ts,cjs,mjs,d.cts,d.mts,jsx,tsx,json,jsonc}"
-      run: bunx @biomejs/biome check --write {staged_files} && git add {staged_files}
+    format:
+      glob: "*.{ts,tsx,json,jsonc}"
+      run: bunx @biomejs/biome check {staged_files} --write && git add {staged_files}
diff --git a/rr/app/lib/db/schema.ts b/rr/app/lib/db/schema.ts
index c169b9f..68c1c8d 100644
--- a/rr/app/lib/db/schema.ts
+++ b/rr/app/lib/db/schema.ts
@@ -35,7 +35,6 @@ export const hai = pgTable("hai", {
 });
 
 // relation between user and haiyama
-// TODO: index
 export const kyoku = pgTable(
 	"kyoku",
 	{
diff --git a/rr/app/lib/store.ts b/rr/app/lib/store.ts
new file mode 100644
index 0000000..618d48f
--- /dev/null
+++ b/rr/app/lib/store.ts
@@ -0,0 +1,65 @@
+import { create } from "zustand";
+import type { Hai } from "./hai";
+import { sortTehai } from "./hai";
+
+interface GameState {
+	kyoku: number;
+	junme: number;
+	haiyama: Hai[];
+	sutehai: Hai[];
+	// Hai * 13
+	tehai: Hai[];
+	// null as an initial value
+	tsumohai: Hai | null;
+}
+
+interface PlayerAction {
+	// tsumo just after tedashi or tsumogiri
+	tedashi: (index: number) => void;
+	tsumogiri: () => void;
+}
+
+const useGameStore = create<GameState & PlayerAction>()((set, get) => ({
+	kyoku: 1,
+	junme: 1,
+	haiyama: [],
+	sutehai: [],
+	tehai: [],
+	tsumohai: null,
+
+	tedashi: (index) => {
+		const state = get();
+		if (!state.tsumohai) {
+			throw new Error("syohai");
+		}
+		const tsumohai = state.tsumohai;
+
+		if (index < 0 || 12 < index) {
+			throw new Error("index out of tehai length");
+		}
+		const deletedTehai = state.tehai.filter((_, i) => i !== index);
+		const discardedHai = state.tehai[index];
+		set(() => ({
+			kyoku: state.kyoku + 1,
+			junme: state.junme + 1,
+			haiyama: state.haiyama.slice(1),
+			sutehai: [...state.sutehai, discardedHai],
+			tehai: sortTehai([...deletedTehai, tsumohai]),
+			tsumohai: state.haiyama[0],
+		}));
+	},
+	tsumogiri: () => {
+		const state = get();
+		if (!state.tsumohai) {
+			throw new Error("syohai");
+		}
+		const tsumohai = state.tsumohai;
+		set(() => ({
+			kyoku: state.kyoku + 1,
+			junme: state.junme + 1,
+			haiyama: state.haiyama.slice(1),
+			sutehai: [...state.sutehai, tsumohai],
+			tsumohai: state.haiyama[0],
+		}));
+	},
+}));
diff --git a/rr/bun.lock b/rr/bun.lock
index 16e659e..2ee8d63 100644
--- a/rr/bun.lock
+++ b/rr/bun.lock
@@ -13,6 +13,7 @@
         "react": "^19.1.1",
         "react-dom": "^19.1.1",
         "react-router": "^7.9.2",
+        "zustand": "^5.0.8",
       },
       "devDependencies": {
         "@cloudflare/vite-plugin": "^1.13.5",
@@ -753,6 +754,8 @@
 
     "zod": ["zod@4.1.12", "", {}, "sha512-JInaHOamG8pt5+Ey8kGmdcAcg3OL9reK8ltczgHTAwNhMys/6ThXHityHxVV2p3fkw/c+MAvBHFVYHFZDmjMCQ=="],
 
+    "zustand": ["zustand@5.0.8", "", { "peerDependencies": { "@types/react": ">=18.0.0", "immer": ">=9.0.6", "react": ">=18.0.0", "use-sync-external-store": ">=1.2.0" }, "optionalPeers": ["@types/react", "immer", "react", "use-sync-external-store"] }, "sha512-gyPKpIaxY9XcO2vSMrLbiER7QMAMGOQZVRdJ6Zi782jkbzZygq5GI9nG8g+sMgitRtndwaBSl7uiqC49o1SSiw=="],
+
     "@babel/core/semver": ["semver@6.3.1", "", { "bin": { "semver": "bin/semver.js" } }, "sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA=="],
 
     "@babel/helper-compilation-targets/semver": ["semver@6.3.1", "", { "bin": { "semver": "bin/semver.js" } }, "sha512-BR7VvDCVHO+q2xBEWskxS6DJE1qRnb7DxzUrogb71CWoSficBxYsiAGd+Kl0mmq/MprG9yArRkyrQxTO6XjMzA=="],
diff --git a/rr/package.json b/rr/package.json
index 4ab5c67..8ce762d 100644
--- a/rr/package.json
+++ b/rr/package.json
@@ -20,7 +20,8 @@
 		"pg": "^8.16.3",
 		"react": "^19.1.1",
 		"react-dom": "^19.1.1",
-		"react-router": "^7.9.2"
+		"react-router": "^7.9.2",
+		"zustand": "^5.0.8"
 	},
 	"devDependencies": {
 		"@cloudflare/vite-plugin": "^1.13.5",