diff --git a/CHANGELOG.md b/CHANGELOG.md
index b959cbbbab..ea1fd23efb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,7 @@
 
 ### Client
 - Enhance: チャットの日本語名称がダイレクトメッセージに戻るとともに、ベータ版機能ではなくなりました
+- Enhance: 画像編集にマスクエフェクトを追加
 - Enhance: 時刻計算のための基準値を一か所で管理するようにし、パフォーマンスを向上
 
 ### Server
diff --git a/locales/index.d.ts b/locales/index.d.ts
index 23f0d88a37..ee808bfa77 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -12378,6 +12378,10 @@ export interface Locale extends ILocale {
              * ティアリング
              */
             "tearing": string;
+            /**
+             * 塗りつぶし(四角)
+             */
+            "fillSquare": string;
         };
         "_fxProps": {
             /**
@@ -12392,6 +12396,10 @@ export interface Locale extends ILocale {
              * サイズ
              */
             "size": string;
+            /**
+             * 位置
+             */
+            "offset": string;
             /**
              * 色
              */
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 3b8f4443b1..322ff3ab2f 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -3314,11 +3314,13 @@ _imageEffector:
     checker: "チェッカー"
     blockNoise: "ブロックノイズ"
     tearing: "ティアリング"
+    fillSquare: "塗りつぶし(四角)"
 
   _fxProps:
     angle: "角度"
     scale: "サイズ"
     size: "サイズ"
+    offset: "位置"
     color: "色"
     opacity: "不透明度"
     normalize: "正規化"
diff --git a/packages/frontend/src/components/MkImageEffectorDialog.vue b/packages/frontend/src/components/MkImageEffectorDialog.vue
index 2c6185fd33..f794af290a 100644
--- a/packages/frontend/src/components/MkImageEffectorDialog.vue
+++ b/packages/frontend/src/components/MkImageEffectorDialog.vue
@@ -19,9 +19,12 @@ SPDX-License-Identifier: AGPL-3.0-only
 	<div :class="$style.root">
 		<div :class="$style.container">
 			<div :class="$style.preview">
-				<canvas ref="canvasEl" :class="$style.previewCanvas"></canvas>
+				<canvas ref="canvasEl" :class="$style.previewCanvas" @pointerdown="onImagePointerdown"></canvas>
 				<div :class="$style.previewContainer">
 					<div class="_acrylic" :class="$style.previewTitle">{{ i18n.ts.preview }}</div>
+					<div class="_acrylic" :class="$style.editControls">
+						<button class="_button" :class="[$style.previewControlsButton, fillSquare ? $style.active : null]" @click="fillSquare = true"><i class="ti ti-pencil"></i></button>
+					</div>
 					<div class="_acrylic" :class="$style.previewControls">
 						<button class="_button" :class="[$style.previewControlsButton, !enabled ? $style.active : null]" @click="enabled = false">Before</button>
 						<button class="_button" :class="[$style.previewControlsButton, enabled ? $style.active : null]" @click="enabled = true">After</button>
@@ -212,6 +215,100 @@ watch(enabled, () => {
 		renderer.render();
 	}
 });
+
+const fillSquare = ref(false);
+
+function onImagePointerdown(ev: PointerEvent) {
+	if (canvasEl.value == null || imageBitmap == null || !fillSquare.value) return;
+
+	const AW = canvasEl.value.clientWidth;
+	const AH = canvasEl.value.clientHeight;
+	const BW = imageBitmap.width;
+	const BH = imageBitmap.height;
+
+	let xOffset = 0;
+	let yOffset = 0;
+
+	if (AW / AH < BW / BH) { // 横長
+		yOffset = AH - BH * (AW / BW);
+	} else { // 縦長
+		xOffset = AW - BW * (AH / BH);
+	}
+
+	xOffset /= 2;
+	yOffset /= 2;
+
+	let startX = ev.offsetX - xOffset;
+	let startY = ev.offsetY - yOffset;
+
+	if (AW / AH < BW / BH) { // 横長
+		startX = startX / (Math.max(AW, AH) / Math.max(BH / BW, 1));
+		startY = startY / (Math.max(AW, AH) / Math.max(BW / BH, 1));
+	} else { // 縦長
+		startX = startX / (Math.min(AW, AH) / Math.max(BH / BW, 1));
+		startY = startY / (Math.min(AW, AH) / Math.max(BW / BH, 1));
+	}
+
+	const id = genId();
+	layers.push({
+		id,
+		fxId: 'fillSquare',
+		params: {
+			offsetX: 0,
+			offsetY: 0,
+			scaleX: 0.1,
+			scaleY: 0.1,
+			angle: 0,
+			opacity: 1,
+			color: [1, 1, 1],
+		},
+	});
+
+	_move(ev.offsetX, ev.offsetY);
+
+	function _move(pointerX: number, pointerY: number) {
+		let x = pointerX - xOffset;
+		let y = pointerY - yOffset;
+
+		if (AW / AH < BW / BH) { // 横長
+			x = x / (Math.max(AW, AH) / Math.max(BH / BW, 1));
+			y = y / (Math.max(AW, AH) / Math.max(BW / BH, 1));
+		} else { // 縦長
+			x = x / (Math.min(AW, AH) / Math.max(BH / BW, 1));
+			y = y / (Math.min(AW, AH) / Math.max(BW / BH, 1));
+		}
+
+		const scaleX = Math.abs(x - startX);
+		const scaleY = Math.abs(y - startY);
+
+		const layerIndex = layers.findIndex((l) => l.id === id);
+		const layer = layerIndex !== -1 ? layers[layerIndex] : null;
+		if (layer != null) {
+			layer.params.offsetX = (x + startX) - 1;
+			layer.params.offsetY = (y + startY) - 1;
+			layer.params.scaleX = scaleX;
+			layer.params.scaleY = scaleY;
+			layers[layerIndex] = layer;
+		}
+	}
+
+	function move(ev: PointerEvent) {
+		_move(ev.offsetX, ev.offsetY);
+	}
+
+	function up() {
+		canvasEl.value?.removeEventListener('pointermove', move);
+		canvasEl.value?.removeEventListener('pointerup', up);
+		canvasEl.value?.removeEventListener('pointercancel', up);
+		canvasEl.value?.releasePointerCapture(ev.pointerId);
+
+		fillSquare.value = false;
+	}
+
+	canvasEl.value.addEventListener('pointermove', move);
+	canvasEl.value.addEventListener('pointerup', up);
+	canvasEl.value.setPointerCapture(ev.pointerId);
+}
 </script>
 
 <style module>
@@ -251,6 +348,18 @@ watch(enabled, () => {
 	font-size: 85%;
 }
 
+.editControls {
+	position: absolute;
+	z-index: 100;
+	bottom: 8px;
+	left: 8px;
+	display: flex;
+	align-items: center;
+	gap: 8px;
+	padding: 6px 10px;
+	border-radius: 6px;
+}
+
 .previewControls {
 	position: absolute;
 	z-index: 100;
@@ -283,9 +392,11 @@ watch(enabled, () => {
 	position: absolute;
 	top: 0;
 	left: 0;
-	width: 100%;
-	height: 100%;
-	padding: 20px;
+	width: -webkit-fill-available;
+	width: stretch;
+	height: -webkit-fill-available;
+	height: stretch;
+	margin: 20px;
 	box-sizing: border-box;
 	object-fit: contain;
 }
diff --git a/packages/frontend/src/utility/image-effector/fxs.ts b/packages/frontend/src/utility/image-effector/fxs.ts
index 1fa48aea15..43e10a22fc 100644
--- a/packages/frontend/src/utility/image-effector/fxs.ts
+++ b/packages/frontend/src/utility/image-effector/fxs.ts
@@ -18,6 +18,7 @@ import { FX_stripe } from './fxs/stripe.js';
 import { FX_threshold } from './fxs/threshold.js';
 import { FX_zoomLines } from './fxs/zoomLines.js';
 import { FX_blockNoise } from './fxs/blockNoise.js';
+import { FX_fillSquare } from './fxs/fillSquare.js';
 import type { ImageEffectorFx } from './ImageEffector.js';
 
 export const FXS = [
@@ -36,4 +37,5 @@ export const FXS = [
 	FX_chromaticAberration,
 	FX_tearing,
 	FX_blockNoise,
+	FX_fillSquare,
 ] as const satisfies ImageEffectorFx<string, any>[];
diff --git a/packages/frontend/src/utility/image-effector/fxs/fillSquare.ts b/packages/frontend/src/utility/image-effector/fxs/fillSquare.ts
new file mode 100644
index 0000000000..55b53830e0
--- /dev/null
+++ b/packages/frontend/src/utility/image-effector/fxs/fillSquare.ts
@@ -0,0 +1,122 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { defineImageEffectorFx } from '../ImageEffector.js';
+import { i18n } from '@/i18n.js';
+
+const shader = `#version 300 es
+precision mediump float;
+
+const float PI = 3.141592653589793;
+const float TWO_PI = 6.283185307179586;
+const float HALF_PI = 1.5707963267948966;
+
+in vec2 in_uv;
+uniform sampler2D in_texture;
+uniform vec2 in_resolution;
+uniform vec2 u_offset;
+uniform vec2 u_scale;
+uniform float u_angle;
+uniform vec3 u_color;
+uniform float u_opacity;
+out vec4 out_color;
+
+void main() {
+	vec4 in_color = texture(in_texture, in_uv);
+	//float x_ratio = max(in_resolution.x / in_resolution.y, 1.0);
+	//float y_ratio = max(in_resolution.y / in_resolution.x, 1.0);
+
+	float angle = -(u_angle * PI);
+	vec2 centeredUv = in_uv - vec2(0.5, 0.5) - u_offset;
+	vec2 rotatedUV = vec2(
+		centeredUv.x * cos(angle) - centeredUv.y * sin(angle),
+		centeredUv.x * sin(angle) + centeredUv.y * cos(angle)
+	) + u_offset;
+
+	bool isInside = rotatedUV.x > u_offset.x - u_scale.x && rotatedUV.x < u_offset.x + u_scale.x && rotatedUV.y > u_offset.y - u_scale.y && rotatedUV.y < u_offset.y + u_scale.y;
+
+	out_color = isInside ? vec4(
+		mix(in_color.r, u_color.r, u_opacity),
+		mix(in_color.g, u_color.g, u_opacity),
+		mix(in_color.b, u_color.b, u_opacity),
+		in_color.a
+	) : in_color;
+}
+`;
+
+export const FX_fillSquare = defineImageEffectorFx({
+	id: 'fillSquare',
+	name: i18n.ts._imageEffector._fxs.fillSquare,
+	shader,
+	uniforms: ['offset', 'scale', 'angle', 'color', 'opacity'] as const,
+	params: {
+		offsetX: {
+			label: i18n.ts._imageEffector._fxProps.offset + ' X',
+			type: 'number',
+			default: 0.0,
+			min: -1.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 100) + '%',
+		},
+		offsetY: {
+			label: i18n.ts._imageEffector._fxProps.offset + ' Y',
+			type: 'number',
+			default: 0.0,
+			min: -1.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 100) + '%',
+		},
+		scaleX: {
+			label: i18n.ts._imageEffector._fxProps.scale + ' X',
+			type: 'number',
+			default: 0.5,
+			min: 0.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 100) + '%',
+		},
+		scaleY: {
+			label: i18n.ts._imageEffector._fxProps.scale + ' Y',
+			type: 'number',
+			default: 0.5,
+			min: 0.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 100) + '%',
+		},
+		angle: {
+			label: i18n.ts._imageEffector._fxProps.angle,
+			type: 'number',
+			default: 0,
+			min: -1.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 90) + '°',
+		},
+		color: {
+			label: i18n.ts._imageEffector._fxProps.color,
+			type: 'color',
+			default: [1, 1, 1],
+		},
+		opacity: {
+			label: i18n.ts._imageEffector._fxProps.opacity,
+			type: 'number',
+			default: 1.0,
+			min: 0.0,
+			max: 1.0,
+			step: 0.01,
+			toViewValue: v => Math.round(v * 100) + '%',
+		},
+	},
+	main: ({ gl, u, params }) => {
+		gl.uniform2f(u.offset, params.offsetX / 2, params.offsetY / 2);
+		gl.uniform2f(u.scale, params.scaleX / 2, params.scaleY / 2);
+		gl.uniform1f(u.angle, params.angle / 2);
+		gl.uniform3f(u.color, params.color[0], params.color[1], params.color[2]);
+		gl.uniform1f(u.opacity, params.opacity);
+	},
+});