diff --git a/packages/frontend/src/pages/drop-and-fusion.vue b/packages/frontend/src/pages/drop-and-fusion.vue
index 482ee7e00..1daf9ddc6 100644
--- a/packages/frontend/src/pages/drop-and-fusion.vue
+++ b/packages/frontend/src/pages/drop-and-fusion.vue
@@ -117,12 +117,9 @@ SPDX-License-Identifier: AGPL-3.0-only
 </template>
 
 <script lang="ts" setup>
-import * as Matter from 'matter-js';
 import { onDeactivated, ref, shallowRef } from 'vue';
-import { EventEmitter } from 'eventemitter3';
 import * as Misskey from 'misskey-js';
 import { definePageMetadata } from '@/scripts/page-metadata.js';
-import * as sound from '@/scripts/sound.js';
 import MkRippleEffect from '@/components/MkRippleEffect.vue';
 import * as os from '@/os.js';
 import MkNumber from '@/components/MkNumber.vue';
@@ -136,19 +133,7 @@ import { useInterval } from '@/scripts/use-interval.js';
 import MkSelect from '@/components/MkSelect.vue';
 import { apiUrl } from '@/config.js';
 import { $i } from '@/account.js';
-
-type Mono = {
-	id: string;
-	level: number;
-	size: number;
-	shape: 'circle' | 'rectangle';
-	score: number;
-	dropCandidate: boolean;
-	sfxPitch: number;
-	img: string;
-	imgSize: number;
-	spriteScale: number;
-};
+import { DropAndFusionGame, Mono } from '@/scripts/drop-and-fusion-engine.js';
 
 const containerEl = shallowRef<HTMLElement>();
 const canvasEl = shallowRef<HTMLCanvasElement>();
@@ -382,7 +367,6 @@ const SQUARE_MONOS: Mono[] = [{
 
 const GAME_WIDTH = 450;
 const GAME_HEIGHT = 600;
-const PHYSICS_QUALITY_FACTOR = 16; // 低いほどパフォーマンスが高いがガタガタして安定しなくなる、逆に高すぎても何故か不安定になる
 
 let viewScaleX = 1;
 let viewScaleY = 1;
@@ -398,373 +382,7 @@ const gameOver = ref(false);
 const gameStarted = ref(false);
 const highScore = ref<number | null>(null);
 
-class Game extends EventEmitter<{
-	changeScore: (newScore: number) => void;
-	changeCombo: (newCombo: number) => void;
-	changeStock: (newStock: { id: string; mono: Mono }[]) => void;
-	dropped: () => void;
-	fusioned: (x: number, y: number, scoreDelta: number) => void;
-	monoAdded: (mono: Mono) => void;
-	gameOver: () => void;
-}> {
-	private COMBO_INTERVAL = 1000;
-	public readonly DROP_INTERVAL = 500;
-	public readonly PLAYAREA_MARGIN = 25;
-	private STOCK_MAX = 4;
-	private loaded = false;
-	private engine: Matter.Engine;
-	private render: Matter.Render;
-	private runner: Matter.Runner;
-	private overflowCollider: Matter.Body;
-	private isGameOver = false;
-
-	private monoDefinitions: Mono[] = [];
-	private monoTextures: Record<string, Blob> = {};
-	private monoTextureUrls: Record<string, string> = {};
-
-	/**
-	 * フィールドに出ていて、かつ合体の対象となるアイテム
-	 */
-	private activeBodyIds: Matter.Body['id'][] = [];
-
-	private latestDroppedBodyId: Matter.Body['id'] | null = null;
-
-	private latestDroppedAt = 0;
-	private latestFusionedAt = 0;
-	private stock: { id: string; mono: Mono }[] = [];
-
-	private _combo = 0;
-	private get combo() {
-		return this._combo;
-	}
-	private set combo(value: number) {
-		this._combo = value;
-		this.emit('changeCombo', value);
-	}
-
-	private _score = 0;
-	private get score() {
-		return this._score;
-	}
-	private set score(value: number) {
-		this._score = value;
-		this.emit('changeScore', value);
-	}
-
-	private comboIntervalId: number | null = null;
-
-	constructor(opts: {
-		monoDefinitions: Mono[];
-	}) {
-		super();
-
-		this.monoDefinitions = opts.monoDefinitions;
-
-		this.engine = Matter.Engine.create({
-			constraintIterations: 2 * PHYSICS_QUALITY_FACTOR,
-			positionIterations: 6 * PHYSICS_QUALITY_FACTOR,
-			velocityIterations: 4 * PHYSICS_QUALITY_FACTOR,
-			gravity: {
-				x: 0,
-				y: 1,
-			},
-			timing: {
-				timeScale: 2,
-			},
-			enableSleeping: false,
-		});
-
-		this.render = Matter.Render.create({
-			engine: this.engine,
-			canvas: canvasEl.value,
-			options: {
-				width: GAME_WIDTH,
-				height: GAME_HEIGHT,
-				background: 'transparent', // transparent to hide
-				wireframeBackground: 'transparent', // transparent to hide
-				wireframes: false,
-				showSleeping: false,
-				pixelRatio: Math.max(2, window.devicePixelRatio),
-			},
-		});
-
-		Matter.Render.run(this.render);
-
-		this.runner = Matter.Runner.create();
-		Matter.Runner.run(this.runner, this.engine);
-
-		this.engine.world.bodies = [];
-
-		//#region walls
-		const WALL_OPTIONS: Matter.IChamferableBodyDefinition = {
-			isStatic: true,
-			friction: 0.7,
-			slop: 1.0,
-			render: {
-				strokeStyle: 'transparent',
-				fillStyle: 'transparent',
-			},
-		};
-
-		const thickness = 100;
-		Matter.Composite.add(this.engine.world, [
-			Matter.Bodies.rectangle(GAME_WIDTH / 2, GAME_HEIGHT + (thickness / 2) - this.PLAYAREA_MARGIN, GAME_WIDTH, thickness, WALL_OPTIONS),
-			Matter.Bodies.rectangle(GAME_WIDTH + (thickness / 2) - this.PLAYAREA_MARGIN, GAME_HEIGHT / 2, thickness, GAME_HEIGHT, WALL_OPTIONS),
-			Matter.Bodies.rectangle(-((thickness / 2) - this.PLAYAREA_MARGIN), GAME_HEIGHT / 2, thickness, GAME_HEIGHT, WALL_OPTIONS),
-		]);
-		//#endregion
-
-		this.overflowCollider = Matter.Bodies.rectangle(GAME_WIDTH / 2, 0, GAME_WIDTH, 200, {
-			isStatic: true,
-			isSensor: true,
-			render: {
-				strokeStyle: 'transparent',
-				fillStyle: 'transparent',
-			},
-		});
-		Matter.Composite.add(this.engine.world, this.overflowCollider);
-
-		// fit the render viewport to the scene
-		Matter.Render.lookAt(this.render, {
-			min: { x: 0, y: 0 },
-			max: { x: GAME_WIDTH, y: GAME_HEIGHT },
-		});
-	}
-
-	private createBody(mono: Mono, x: number, y: number) {
-		const options: Matter.IBodyDefinition = {
-			label: mono.id,
-			//density: 0.0005,
-			density: mono.size / 1000,
-			restitution: 0.2,
-			frictionAir: 0.01,
-			friction: 0.7,
-			frictionStatic: 5,
-			slop: 1.0,
-			//mass: 0,
-			render: {
-				sprite: {
-					texture: mono.img,
-					xScale: (mono.size / mono.imgSize) * mono.spriteScale,
-					yScale: (mono.size / mono.imgSize) * mono.spriteScale,
-				},
-			},
-		};
-		if (mono.shape === 'circle') {
-			return Matter.Bodies.circle(x, y, mono.size / 2, options);
-		} else if (mono.shape === 'rectangle') {
-			return Matter.Bodies.rectangle(x, y, mono.size, mono.size, options);
-		} else {
-			throw new Error('unrecognized shape');
-		}
-	}
-
-	private fusion(bodyA: Matter.Body, bodyB: Matter.Body) {
-		const now = Date.now();
-		if (this.latestFusionedAt > now - this.COMBO_INTERVAL) {
-			this.combo++;
-		} else {
-			this.combo = 1;
-		}
-		this.latestFusionedAt = now;
-
-		// TODO: 単に位置だけでなくそれぞれの動きベクトルも融合する
-		const newX = (bodyA.position.x + bodyB.position.x) / 2;
-		const newY = (bodyA.position.y + bodyB.position.y) / 2;
-
-		Matter.Composite.remove(this.engine.world, [bodyA, bodyB]);
-		this.activeBodyIds = this.activeBodyIds.filter(x => x !== bodyA.id && x !== bodyB.id);
-
-		const currentMono = this.monoDefinitions.find(y => y.id === bodyA.label)!;
-		const nextMono = this.monoDefinitions.find(x => x.level === currentMono.level + 1);
-
-		if (nextMono) {
-			const body = this.createBody(nextMono, newX, newY);
-			Matter.Composite.add(this.engine.world, body);
-
-			// 連鎖してfusionした場合の分かりやすさのため少し間を置いてからfusion対象になるようにする
-			window.setTimeout(() => {
-				this.activeBodyIds.push(body.id);
-			}, 100);
-
-			const comboBonus = 1 + ((this.combo - 1) / 5);
-			const additionalScore = Math.round(currentMono.score * comboBonus);
-			this.score += additionalScore;
-
-			const pan = ((newX / GAME_WIDTH) - 0.5) * 2;
-			sound.playRaw('syuilo/bubble2', 1, pan, nextMono.sfxPitch);
-
-			this.emit('monoAdded', nextMono);
-			this.emit('fusioned', newX, newY, additionalScore);
-		} else {
-			//const VELOCITY = 30;
-			//for (let i = 0; i < 10; i++) {
-			//	const body = createBody(FRUITS.find(x => x.level === (1 + Math.floor(Math.random() * 3)))!, x + ((Math.random() * VELOCITY) - (VELOCITY / 2)), y + ((Math.random() * VELOCITY) - (VELOCITY / 2)));
-			//	Matter.Composite.add(world, body);
-			//	bodies.push(body);
-			//}
-			//sound.playRaw({
-			//	type: 'syuilo/bubble2',
-			//	volume: 1,
-			//});
-		}
-	}
-
-	private gameOver() {
-		this.isGameOver = true;
-		Matter.Runner.stop(this.runner);
-		this.emit('gameOver');
-	}
-
-	/** テクスチャをすべてキャッシュする */
-	private async loadMonoTextures() {
-		async function loadSingleMonoTexture(mono: Mono, game: Game) {
-			// Matter-js内にキャッシュがある場合はスキップ
-			if (game.render.textures[mono.img]) return;
-			console.log('loading', mono.img);
-
-			let src = mono.img;
-			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-			if (game.monoTextureUrls[mono.img]) {
-				src = game.monoTextureUrls[mono.img];
-			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-			} else if (game.monoTextures[mono.img]) {
-				src = URL.createObjectURL(game.monoTextures[mono.img]);
-				game.monoTextureUrls[mono.img] = src;
-			} else {
-				const res = await fetch(mono.img);
-				const blob = await res.blob();
-				game.monoTextures[mono.img] = blob;
-				src = URL.createObjectURL(blob);
-				game.monoTextureUrls[mono.img] = src;
-			}
-
-			const image = new Image();
-			image.src = src;
-			game.render.textures[mono.img] = image;
-		}
-
-		return Promise.all(this.monoDefinitions.map(x => loadSingleMonoTexture(x, this)));
-	}
-
-	public start() {
-		if (!this.loaded) throw new Error('game is not loaded yet');
-
-		for (let i = 0; i < this.STOCK_MAX; i++) {
-			this.stock.push({
-				id: Math.random().toString(),
-				mono: this.monoDefinitions.filter(x => x.dropCandidate)[Math.floor(Math.random() * this.monoDefinitions.filter(x => x.dropCandidate).length)],
-			});
-		}
-		this.emit('changeStock', this.stock);
-
-		// TODO: fusion予約状態のアイテムは光らせるなどの演出をすると楽しそう
-		let fusionReservedPairs: { bodyA: Matter.Body; bodyB: Matter.Body }[] = [];
-
-		const minCollisionEnergyForSound = 2.5;
-		const maxCollisionEnergyForSound = 9;
-		const soundPitchMax = 4;
-		const soundPitchMin = 0.5;
-
-		Matter.Events.on(this.engine, 'collisionStart', (event) => {
-			for (const pairs of event.pairs) {
-				const { bodyA, bodyB } = pairs;
-				if (bodyA.id === this.overflowCollider.id || bodyB.id === this.overflowCollider.id) {
-					if (bodyA.id === this.latestDroppedBodyId || bodyB.id === this.latestDroppedBodyId) {
-						continue;
-					}
-					this.gameOver();
-					break;
-				}
-				const shouldFusion = (bodyA.label === bodyB.label) && !fusionReservedPairs.some(x => x.bodyA.id === bodyA.id || x.bodyA.id === bodyB.id || x.bodyB.id === bodyA.id || x.bodyB.id === bodyB.id);
-				if (shouldFusion) {
-					if (this.activeBodyIds.includes(bodyA.id) && this.activeBodyIds.includes(bodyB.id)) {
-						this.fusion(bodyA, bodyB);
-					} else {
-						fusionReservedPairs.push({ bodyA, bodyB });
-						window.setTimeout(() => {
-							fusionReservedPairs = fusionReservedPairs.filter(x => x.bodyA.id !== bodyA.id && x.bodyB.id !== bodyB.id);
-							this.fusion(bodyA, bodyB);
-						}, 100);
-					}
-				} else {
-					const energy = pairs.collision.depth;
-					if (energy > minCollisionEnergyForSound) {
-						const vol = (Math.min(maxCollisionEnergyForSound, energy - minCollisionEnergyForSound) / maxCollisionEnergyForSound) / 4;
-						const pan = ((((bodyA.position.x + bodyB.position.x) / 2) / GAME_WIDTH) - 0.5) * 2;
-						const pitch = soundPitchMin + ((soundPitchMax - soundPitchMin) * (1 - (Math.min(10, energy) / 10)));
-						sound.playRaw('syuilo/poi1', vol, pan, pitch);
-					}
-				}
-			}
-		});
-
-		this.comboIntervalId = window.setInterval(() => {
-			if (this.latestFusionedAt < Date.now() - this.COMBO_INTERVAL) {
-				this.combo = 0;
-			}
-		}, 500);
-	}
-
-	public async load() {
-		await this.loadMonoTextures();
-		this.loaded = true;
-	}
-
-	public getTextureImageUrl(mono: Mono) {
-		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-		if (this.monoTextureUrls[mono.img]) {
-			return this.monoTextureUrls[mono.img];
-
-		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
-		} else if (this.monoTextures[mono.img]) {
-			// Gameクラス内にキャッシュがある場合はそれを使う
-			const out = URL.createObjectURL(this.monoTextures[mono.img]);
-			this.monoTextureUrls[mono.img] = out;
-			return out;
-		} else {
-			return mono.img;
-		}
-	}
-
-	public getActiveMonos() {
-		return this.engine.world.bodies.map(x => this.monoDefinitions.find((mono) => mono.id === x.label)!).filter(x => x !== undefined);
-	}
-
-	public drop(_x: number) {
-		if (this.isGameOver) return;
-		if (Date.now() - this.latestDroppedAt < this.DROP_INTERVAL) {
-			return;
-		}
-		const st = this.stock.shift()!;
-		this.stock.push({
-			id: Math.random().toString(),
-			mono: this.monoDefinitions.filter(x => x.dropCandidate)[Math.floor(Math.random() * this.monoDefinitions.filter(x => x.dropCandidate).length)],
-		});
-		this.emit('changeStock', this.stock);
-
-		const x = Math.min(GAME_WIDTH - this.PLAYAREA_MARGIN - (st.mono.size / 2), Math.max(this.PLAYAREA_MARGIN + (st.mono.size / 2), _x));
-		const body = this.createBody(st.mono, x, 50 + st.mono.size / 2);
-		Matter.Composite.add(this.engine.world, body);
-		this.activeBodyIds.push(body.id);
-		this.latestDroppedBodyId = body.id;
-		this.latestDroppedAt = Date.now();
-		this.emit('dropped');
-		this.emit('monoAdded', st.mono);
-		const pan = ((x / GAME_WIDTH) - 0.5) * 2;
-		sound.playRaw('syuilo/poi2', 1, pan);
-	}
-
-	public dispose() {
-		if (this.comboIntervalId) window.clearInterval(this.comboIntervalId);
-		Matter.Render.stop(this.render);
-		Matter.Runner.stop(this.runner);
-		Matter.World.clear(this.engine.world, false);
-		Matter.Engine.clear(this.engine);
-	}
-}
-
-let game: Game;
+let game: DropAndFusionGame;
 let containerElRect: DOMRect | null = null;
 
 function onClick(ev: MouseEvent) {
@@ -885,10 +503,17 @@ async function start() {
 		highScore.value = null;
 	}
 
-	game = new Game(gameMode.value === 'normal' ? {
-		monoDefinitions: NORAML_MONOS,
-	} : {
-		monoDefinitions: SQUARE_MONOS,
+	game = new DropAndFusionGame({
+		width: GAME_WIDTH,
+		height: GAME_HEIGHT,
+		canvas: canvasEl.value!,
+		...(
+			gameMode.value === 'normal' ? {
+				monoDefinitions: NORAML_MONOS,
+			} : {
+				monoDefinitions: SQUARE_MONOS,
+			}
+		),
 	});
 	attachGameEvents();
 	os.promiseDialog(game.load(), () => {
diff --git a/packages/frontend/src/scripts/drop-and-fusion-engine.ts b/packages/frontend/src/scripts/drop-and-fusion-engine.ts
new file mode 100644
index 000000000..7241525a3
--- /dev/null
+++ b/packages/frontend/src/scripts/drop-and-fusion-engine.ts
@@ -0,0 +1,396 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and other misskey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { EventEmitter } from 'eventemitter3';
+import * as Matter from 'matter-js';
+import * as sound from '@/scripts/sound.js';
+
+export type Mono = {
+	id: string;
+	level: number;
+	size: number;
+	shape: 'circle' | 'rectangle';
+	score: number;
+	dropCandidate: boolean;
+	sfxPitch: number;
+	img: string;
+	imgSize: number;
+	spriteScale: number;
+};
+
+const PHYSICS_QUALITY_FACTOR = 16; // 低いほどパフォーマンスが高いがガタガタして安定しなくなる、逆に高すぎても何故か不安定になる
+
+export class DropAndFusionGame extends EventEmitter<{
+	changeScore: (newScore: number) => void;
+	changeCombo: (newCombo: number) => void;
+	changeStock: (newStock: { id: string; mono: Mono }[]) => void;
+	dropped: () => void;
+	fusioned: (x: number, y: number, scoreDelta: number) => void;
+	monoAdded: (mono: Mono) => void;
+	gameOver: () => void;
+}> {
+	private COMBO_INTERVAL = 1000;
+	public readonly DROP_INTERVAL = 500;
+	public readonly PLAYAREA_MARGIN = 25;
+	private STOCK_MAX = 4;
+	private loaded = false;
+	private engine: Matter.Engine;
+	private render: Matter.Render;
+	private runner: Matter.Runner;
+	private overflowCollider: Matter.Body;
+	private isGameOver = false;
+
+	private gameWidth: number;
+	private gameHeight: number;
+	private monoDefinitions: Mono[] = [];
+	private monoTextures: Record<string, Blob> = {};
+	private monoTextureUrls: Record<string, string> = {};
+
+	/**
+	 * フィールドに出ていて、かつ合体の対象となるアイテム
+	 */
+	private activeBodyIds: Matter.Body['id'][] = [];
+
+	private latestDroppedBodyId: Matter.Body['id'] | null = null;
+
+	private latestDroppedAt = 0;
+	private latestFusionedAt = 0;
+	private stock: { id: string; mono: Mono }[] = [];
+
+	private _combo = 0;
+	private get combo() {
+		return this._combo;
+	}
+	private set combo(value: number) {
+		this._combo = value;
+		this.emit('changeCombo', value);
+	}
+
+	private _score = 0;
+	private get score() {
+		return this._score;
+	}
+	private set score(value: number) {
+		this._score = value;
+		this.emit('changeScore', value);
+	}
+
+	private comboIntervalId: number | null = null;
+
+	constructor(opts: {
+		canvas: HTMLCanvasElement;
+		width: number;
+		height: number;
+		monoDefinitions: Mono[];
+	}) {
+		super();
+
+		this.gameWidth = opts.width;
+		this.gameHeight = opts.height;
+		this.monoDefinitions = opts.monoDefinitions;
+
+		this.engine = Matter.Engine.create({
+			constraintIterations: 2 * PHYSICS_QUALITY_FACTOR,
+			positionIterations: 6 * PHYSICS_QUALITY_FACTOR,
+			velocityIterations: 4 * PHYSICS_QUALITY_FACTOR,
+			gravity: {
+				x: 0,
+				y: 1,
+			},
+			timing: {
+				timeScale: 2,
+			},
+			enableSleeping: false,
+		});
+
+		this.render = Matter.Render.create({
+			engine: this.engine,
+			canvas: opts.canvas,
+			options: {
+				width: this.gameWidth,
+				height: this.gameHeight,
+				background: 'transparent', // transparent to hide
+				wireframeBackground: 'transparent', // transparent to hide
+				wireframes: false,
+				showSleeping: false,
+				pixelRatio: Math.max(2, window.devicePixelRatio),
+			},
+		});
+
+		Matter.Render.run(this.render);
+
+		this.runner = Matter.Runner.create();
+		Matter.Runner.run(this.runner, this.engine);
+
+		this.engine.world.bodies = [];
+
+		//#region walls
+		const WALL_OPTIONS: Matter.IChamferableBodyDefinition = {
+			isStatic: true,
+			friction: 0.7,
+			slop: 1.0,
+			render: {
+				strokeStyle: 'transparent',
+				fillStyle: 'transparent',
+			},
+		};
+
+		const thickness = 100;
+		Matter.Composite.add(this.engine.world, [
+			Matter.Bodies.rectangle(this.gameWidth / 2, this.gameHeight + (thickness / 2) - this.PLAYAREA_MARGIN, this.gameWidth, thickness, WALL_OPTIONS),
+			Matter.Bodies.rectangle(this.gameWidth + (thickness / 2) - this.PLAYAREA_MARGIN, this.gameHeight / 2, thickness, this.gameHeight, WALL_OPTIONS),
+			Matter.Bodies.rectangle(-((thickness / 2) - this.PLAYAREA_MARGIN), this.gameHeight / 2, thickness, this.gameHeight, WALL_OPTIONS),
+		]);
+		//#endregion
+
+		this.overflowCollider = Matter.Bodies.rectangle(this.gameWidth / 2, 0, this.gameWidth, 200, {
+			isStatic: true,
+			isSensor: true,
+			render: {
+				strokeStyle: 'transparent',
+				fillStyle: 'transparent',
+			},
+		});
+		Matter.Composite.add(this.engine.world, this.overflowCollider);
+
+		// fit the render viewport to the scene
+		Matter.Render.lookAt(this.render, {
+			min: { x: 0, y: 0 },
+			max: { x: this.gameWidth, y: this.gameHeight },
+		});
+	}
+
+	private createBody(mono: Mono, x: number, y: number) {
+		const options: Matter.IBodyDefinition = {
+			label: mono.id,
+			//density: 0.0005,
+			density: mono.size / 1000,
+			restitution: 0.2,
+			frictionAir: 0.01,
+			friction: 0.7,
+			frictionStatic: 5,
+			slop: 1.0,
+			//mass: 0,
+			render: {
+				sprite: {
+					texture: mono.img,
+					xScale: (mono.size / mono.imgSize) * mono.spriteScale,
+					yScale: (mono.size / mono.imgSize) * mono.spriteScale,
+				},
+			},
+		};
+		if (mono.shape === 'circle') {
+			return Matter.Bodies.circle(x, y, mono.size / 2, options);
+		} else if (mono.shape === 'rectangle') {
+			return Matter.Bodies.rectangle(x, y, mono.size, mono.size, options);
+		} else {
+			throw new Error('unrecognized shape');
+		}
+	}
+
+	private fusion(bodyA: Matter.Body, bodyB: Matter.Body) {
+		const now = Date.now();
+		if (this.latestFusionedAt > now - this.COMBO_INTERVAL) {
+			this.combo++;
+		} else {
+			this.combo = 1;
+		}
+		this.latestFusionedAt = now;
+
+		// TODO: 単に位置だけでなくそれぞれの動きベクトルも融合する
+		const newX = (bodyA.position.x + bodyB.position.x) / 2;
+		const newY = (bodyA.position.y + bodyB.position.y) / 2;
+
+		Matter.Composite.remove(this.engine.world, [bodyA, bodyB]);
+		this.activeBodyIds = this.activeBodyIds.filter(x => x !== bodyA.id && x !== bodyB.id);
+
+		const currentMono = this.monoDefinitions.find(y => y.id === bodyA.label)!;
+		const nextMono = this.monoDefinitions.find(x => x.level === currentMono.level + 1);
+
+		if (nextMono) {
+			const body = this.createBody(nextMono, newX, newY);
+			Matter.Composite.add(this.engine.world, body);
+
+			// 連鎖してfusionした場合の分かりやすさのため少し間を置いてからfusion対象になるようにする
+			window.setTimeout(() => {
+				this.activeBodyIds.push(body.id);
+			}, 100);
+
+			const comboBonus = 1 + ((this.combo - 1) / 5);
+			const additionalScore = Math.round(currentMono.score * comboBonus);
+			this.score += additionalScore;
+
+			const pan = ((newX / this.gameWidth) - 0.5) * 2;
+			sound.playRaw('syuilo/bubble2', 1, pan, nextMono.sfxPitch);
+
+			this.emit('monoAdded', nextMono);
+			this.emit('fusioned', newX, newY, additionalScore);
+		} else {
+			//const VELOCITY = 30;
+			//for (let i = 0; i < 10; i++) {
+			//	const body = createBody(FRUITS.find(x => x.level === (1 + Math.floor(Math.random() * 3)))!, x + ((Math.random() * VELOCITY) - (VELOCITY / 2)), y + ((Math.random() * VELOCITY) - (VELOCITY / 2)));
+			//	Matter.Composite.add(world, body);
+			//	bodies.push(body);
+			//}
+			//sound.playRaw({
+			//	type: 'syuilo/bubble2',
+			//	volume: 1,
+			//});
+		}
+	}
+
+	private gameOver() {
+		this.isGameOver = true;
+		Matter.Runner.stop(this.runner);
+		this.emit('gameOver');
+	}
+
+	/** テクスチャをすべてキャッシュする */
+	private async loadMonoTextures() {
+		async function loadSingleMonoTexture(mono: Mono, game: DropAndFusionGame) {
+			// Matter-js内にキャッシュがある場合はスキップ
+			if (game.render.textures[mono.img]) return;
+			console.log('loading', mono.img);
+
+			let src = mono.img;
+			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+			if (game.monoTextureUrls[mono.img]) {
+				src = game.monoTextureUrls[mono.img];
+			// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+			} else if (game.monoTextures[mono.img]) {
+				src = URL.createObjectURL(game.monoTextures[mono.img]);
+				game.monoTextureUrls[mono.img] = src;
+			} else {
+				const res = await fetch(mono.img);
+				const blob = await res.blob();
+				game.monoTextures[mono.img] = blob;
+				src = URL.createObjectURL(blob);
+				game.monoTextureUrls[mono.img] = src;
+			}
+
+			const image = new Image();
+			image.src = src;
+			game.render.textures[mono.img] = image;
+		}
+
+		return Promise.all(this.monoDefinitions.map(x => loadSingleMonoTexture(x, this)));
+	}
+
+	public start() {
+		if (!this.loaded) throw new Error('game is not loaded yet');
+
+		for (let i = 0; i < this.STOCK_MAX; i++) {
+			this.stock.push({
+				id: Math.random().toString(),
+				mono: this.monoDefinitions.filter(x => x.dropCandidate)[Math.floor(Math.random() * this.monoDefinitions.filter(x => x.dropCandidate).length)],
+			});
+		}
+		this.emit('changeStock', this.stock);
+
+		// TODO: fusion予約状態のアイテムは光らせるなどの演出をすると楽しそう
+		let fusionReservedPairs: { bodyA: Matter.Body; bodyB: Matter.Body }[] = [];
+
+		const minCollisionEnergyForSound = 2.5;
+		const maxCollisionEnergyForSound = 9;
+		const soundPitchMax = 4;
+		const soundPitchMin = 0.5;
+
+		Matter.Events.on(this.engine, 'collisionStart', (event) => {
+			for (const pairs of event.pairs) {
+				const { bodyA, bodyB } = pairs;
+				if (bodyA.id === this.overflowCollider.id || bodyB.id === this.overflowCollider.id) {
+					if (bodyA.id === this.latestDroppedBodyId || bodyB.id === this.latestDroppedBodyId) {
+						continue;
+					}
+					this.gameOver();
+					break;
+				}
+				const shouldFusion = (bodyA.label === bodyB.label) && !fusionReservedPairs.some(x => x.bodyA.id === bodyA.id || x.bodyA.id === bodyB.id || x.bodyB.id === bodyA.id || x.bodyB.id === bodyB.id);
+				if (shouldFusion) {
+					if (this.activeBodyIds.includes(bodyA.id) && this.activeBodyIds.includes(bodyB.id)) {
+						this.fusion(bodyA, bodyB);
+					} else {
+						fusionReservedPairs.push({ bodyA, bodyB });
+						window.setTimeout(() => {
+							fusionReservedPairs = fusionReservedPairs.filter(x => x.bodyA.id !== bodyA.id && x.bodyB.id !== bodyB.id);
+							this.fusion(bodyA, bodyB);
+						}, 100);
+					}
+				} else {
+					const energy = pairs.collision.depth;
+					if (energy > minCollisionEnergyForSound) {
+						const vol = (Math.min(maxCollisionEnergyForSound, energy - minCollisionEnergyForSound) / maxCollisionEnergyForSound) / 4;
+						const pan = ((((bodyA.position.x + bodyB.position.x) / 2) / this.gameWidth) - 0.5) * 2;
+						const pitch = soundPitchMin + ((soundPitchMax - soundPitchMin) * (1 - (Math.min(10, energy) / 10)));
+						sound.playRaw('syuilo/poi1', vol, pan, pitch);
+					}
+				}
+			}
+		});
+
+		this.comboIntervalId = window.setInterval(() => {
+			if (this.latestFusionedAt < Date.now() - this.COMBO_INTERVAL) {
+				this.combo = 0;
+			}
+		}, 500);
+	}
+
+	public async load() {
+		await this.loadMonoTextures();
+		this.loaded = true;
+	}
+
+	public getTextureImageUrl(mono: Mono) {
+		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+		if (this.monoTextureUrls[mono.img]) {
+			return this.monoTextureUrls[mono.img];
+
+		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+		} else if (this.monoTextures[mono.img]) {
+			// Gameクラス内にキャッシュがある場合はそれを使う
+			const out = URL.createObjectURL(this.monoTextures[mono.img]);
+			this.monoTextureUrls[mono.img] = out;
+			return out;
+		} else {
+			return mono.img;
+		}
+	}
+
+	public getActiveMonos() {
+		return this.engine.world.bodies.map(x => this.monoDefinitions.find((mono) => mono.id === x.label)!).filter(x => x !== undefined);
+	}
+
+	public drop(_x: number) {
+		if (this.isGameOver) return;
+		if (Date.now() - this.latestDroppedAt < this.DROP_INTERVAL) {
+			return;
+		}
+		const st = this.stock.shift()!;
+		this.stock.push({
+			id: Math.random().toString(),
+			mono: this.monoDefinitions.filter(x => x.dropCandidate)[Math.floor(Math.random() * this.monoDefinitions.filter(x => x.dropCandidate).length)],
+		});
+		this.emit('changeStock', this.stock);
+
+		const x = Math.min(this.gameWidth - this.PLAYAREA_MARGIN - (st.mono.size / 2), Math.max(this.PLAYAREA_MARGIN + (st.mono.size / 2), _x));
+		const body = this.createBody(st.mono, x, 50 + st.mono.size / 2);
+		Matter.Composite.add(this.engine.world, body);
+		this.activeBodyIds.push(body.id);
+		this.latestDroppedBodyId = body.id;
+		this.latestDroppedAt = Date.now();
+		this.emit('dropped');
+		this.emit('monoAdded', st.mono);
+		const pan = ((x / this.gameWidth) - 0.5) * 2;
+		sound.playRaw('syuilo/poi2', 1, pan);
+	}
+
+	public dispose() {
+		if (this.comboIntervalId) window.clearInterval(this.comboIntervalId);
+		Matter.Render.stop(this.render);
+		Matter.Runner.stop(this.runner);
+		Matter.World.clear(this.engine.world, false);
+		Matter.Engine.clear(this.engine);
+	}
+}