diff --git a/locales/index.d.ts b/locales/index.d.ts
index 440f24ac84..66fe6615ff 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -5218,6 +5218,31 @@ export interface Locale extends ILocale {
      * 利用可能なロール
      */
     "availableRoles": string;
+    /**
+     * クライアント設定の初期値
+     */
+    "clientSettingOverrides": string;
+    /**
+     * 全ユーザーに対するクライアント設定の初期値を変更できます。
+     * 知識のない方が変更すると全ユーザーがクライアントにアクセスできなくなる可能性があります。
+     */
+    "clientSettingOverridesWarn": string;
+    /**
+     * オーバーライドする
+     */
+    "enableOverride": string;
+    /**
+     * オーバーライドする値
+     */
+    "overrideValue": string;
+    /**
+     * スイッチをオンにするとtrueとなります。
+     */
+    "onToTrue": string;
+    /**
+     * リセット
+     */
+    "reset": string;
     "_accountSettings": {
         /**
          * コンテンツの表示にログインを必須にする
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 5d8e1a5e72..10923ed414 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -1300,6 +1300,12 @@ thisContentsAreMarkedAsSigninRequiredByAuthor: "投稿者により、表示に
 lockdown: "ロックダウン"
 pleaseSelectAccount: "アカウントを選択してください"
 availableRoles: "利用可能なロール"
+clientSettingOverrides: "クライアント設定の初期値"
+clientSettingOverridesWarn: "全ユーザーに対するクライアント設定の初期値を変更できます。\n知識のない方が変更すると全ユーザーがクライアントにアクセスできなくなる可能性があります。"
+enableOverride: "オーバーライドする"
+overrideValue: "オーバーライドする値"
+onToTrue: "スイッチをオンにするとtrueとなります。"
+reset: "リセット"
 
 _accountSettings:
   requireSigninToViewContents: "コンテンツの表示にログインを必須にする"
diff --git a/packages/backend/migration/1730552981368-ClientSettingOverrides.js b/packages/backend/migration/1730552981368-ClientSettingOverrides.js
new file mode 100644
index 0000000000..456d8305d5
--- /dev/null
+++ b/packages/backend/migration/1730552981368-ClientSettingOverrides.js
@@ -0,0 +1,16 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export class ClientSettingOverrides1730552981368 {
+	name = 'ClientSettingOverrides1730552981368'
+
+	async up(queryRunner) {
+		await queryRunner.query(`ALTER TABLE "meta" ADD "defaultClientSettingOverrides" character varying(8192)`);
+	}
+
+	async down(queryRunner) {
+		await queryRunner.query(`ALTER TABLE "meta" DROP COLUMN "defaultClientSettingOverrides"`);
+	}
+}
diff --git a/packages/backend/src/core/entities/MetaEntityService.ts b/packages/backend/src/core/entities/MetaEntityService.ts
index 409dca3426..39db1ccf6c 100644
--- a/packages/backend/src/core/entities/MetaEntityService.ts
+++ b/packages/backend/src/core/entities/MetaEntityService.ts
@@ -151,6 +151,7 @@ export class MetaEntityService {
 
 		const packDetailed: Packed<'MetaDetailed'> = {
 			...packed,
+			defaultClientSettingOverrides: instance.defaultClientSettingOverrides,
 			cacheRemoteFiles: instance.cacheRemoteFiles,
 			cacheRemoteSensitiveFiles: instance.cacheRemoteSensitiveFiles,
 			requireSetup: !await this.instanceActorService.realLocalUsersPresent(),
diff --git a/packages/backend/src/models/Meta.ts b/packages/backend/src/models/Meta.ts
index ad5e31ad6f..f61229cb01 100644
--- a/packages/backend/src/models/Meta.ts
+++ b/packages/backend/src/models/Meta.ts
@@ -409,6 +409,12 @@ export class MiMeta {
 	})
 	public defaultDarkTheme: string | null;
 
+	@Column('varchar', {
+		length: 8192,
+		nullable: true,
+	})
+	public defaultClientSettingOverrides: string | null;
+
 	@Column('boolean', {
 		default: false,
 	})
diff --git a/packages/backend/src/models/json-schema/meta.ts b/packages/backend/src/models/json-schema/meta.ts
index e3fd63464a..49b8f97272 100644
--- a/packages/backend/src/models/json-schema/meta.ts
+++ b/packages/backend/src/models/json-schema/meta.ts
@@ -315,6 +315,10 @@ export const packedMetaDetailedOnlySchema = {
 				},
 			},
 		},
+		defaultClientSettingOverrides: {
+			type: 'string',
+			optional: false, nullable: true,
+		},
 		proxyAccountName: {
 			type: 'string',
 			optional: false, nullable: true,
diff --git a/packages/backend/src/server/api/endpoints/admin/meta.ts b/packages/backend/src/server/api/endpoints/admin/meta.ts
index 64e3cc33bd..beae8473aa 100644
--- a/packages/backend/src/server/api/endpoints/admin/meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/meta.ts
@@ -420,6 +420,10 @@ export const meta = {
 				type: 'string',
 				optional: false, nullable: true,
 			},
+			defaultClientSettingOverrides: {
+				type: 'string',
+				optional: false, nullable: true,
+			},
 			description: {
 				type: 'string',
 				optional: false, nullable: true,
@@ -585,6 +589,7 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				logoImageUrl: instance.logoImageUrl,
 				defaultLightTheme: instance.defaultLightTheme,
 				defaultDarkTheme: instance.defaultDarkTheme,
+				defaultClientSettingOverrides: instance.defaultClientSettingOverrides,
 				enableEmail: instance.enableEmail,
 				enableServiceWorker: instance.enableServiceWorker,
 				translatorAvailable: instance.deeplAuthKey != null,
diff --git a/packages/backend/src/server/api/endpoints/admin/update-meta.ts b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
index 38ef0d1de8..16d37a1d68 100644
--- a/packages/backend/src/server/api/endpoints/admin/update-meta.ts
+++ b/packages/backend/src/server/api/endpoints/admin/update-meta.ts
@@ -67,6 +67,7 @@ export const paramDef = {
 		description: { type: 'string', nullable: true },
 		defaultLightTheme: { type: 'string', nullable: true },
 		defaultDarkTheme: { type: 'string', nullable: true },
+		defaultClientSettingOverrides: { type: 'string', nullable: true },
 		cacheRemoteFiles: { type: 'boolean' },
 		cacheRemoteSensitiveFiles: { type: 'boolean' },
 		emailRequiredForSignup: { type: 'boolean' },
@@ -303,6 +304,10 @@ export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-
 				set.defaultDarkTheme = ps.defaultDarkTheme;
 			}
 
+			if (ps.defaultClientSettingOverrides !== undefined) {
+				set.defaultClientSettingOverrides = ps.defaultClientSettingOverrides;
+			}
+
 			if (ps.cacheRemoteFiles !== undefined) {
 				set.cacheRemoteFiles = ps.cacheRemoteFiles;
 			}
diff --git a/packages/frontend/src/boot/common.ts b/packages/frontend/src/boot/common.ts
index 90ae49ee59..0f2824a180 100644
--- a/packages/frontend/src/boot/common.ts
+++ b/packages/frontend/src/boot/common.ts
@@ -14,7 +14,7 @@ import { isDeviceDarkmode } from '@/scripts/is-device-darkmode.js';
 import { updateI18n, i18n } from '@/i18n.js';
 import { $i, refreshAccount, login } from '@/account.js';
 import { defaultStore, ColdDeviceStorage } from '@/store.js';
-import { fetchInstance, instance } from '@/instance.js';
+import { initInstance, instance } from '@/instance.js';
 import { deviceKind } from '@/scripts/device-kind.js';
 import { reloadChannel } from '@/scripts/unison-reload.js';
 import { getUrlWithoutLoginId } from '@/scripts/login-id.js';
@@ -115,15 +115,12 @@ export async function common(createVue: () => App<Element>) {
 	const html = document.documentElement;
 	html.setAttribute('lang', lang);
 	//#endregion
-
+	
+	await initInstance();
 	await defaultStore.ready;
 	await deckStore.ready;
 
-	const fetchInstanceMetaPromise = fetchInstance();
-
-	fetchInstanceMetaPromise.then(() => {
-		miLocalStorage.setItem('v', instance.version);
-	});
+	miLocalStorage.setItem('v', instance.version);
 
 	//#region loginId
 	const params = new URLSearchParams(location.search);
@@ -177,13 +174,11 @@ export async function common(createVue: () => App<Element>) {
 	});
 	//#endregion
 
-	fetchInstanceMetaPromise.then(() => {
-		if (defaultStore.state.themeInitial) {
-			if (instance.defaultLightTheme != null) ColdDeviceStorage.set('lightTheme', JSON.parse(instance.defaultLightTheme));
-			if (instance.defaultDarkTheme != null) ColdDeviceStorage.set('darkTheme', JSON.parse(instance.defaultDarkTheme));
-			defaultStore.set('themeInitial', false);
-		}
-	});
+	if (defaultStore.state.themeInitial) {
+		if (instance.defaultLightTheme != null) ColdDeviceStorage.set('lightTheme', JSON.parse(instance.defaultLightTheme));
+		if (instance.defaultDarkTheme != null) ColdDeviceStorage.set('darkTheme', JSON.parse(instance.defaultDarkTheme));
+		defaultStore.set('themeInitial', false);
+	}
 
 	watch(defaultStore.reactiveState.useBlurEffectForModal, v => {
 		document.documentElement.style.setProperty('--MI-modalBgFilter', v ? 'blur(4px)' : 'none');
diff --git a/packages/frontend/src/instance.ts b/packages/frontend/src/instance.ts
index 71cb42b30c..9717c08f4d 100644
--- a/packages/frontend/src/instance.ts
+++ b/packages/frontend/src/instance.ts
@@ -16,7 +16,7 @@ const providedMetaEl = document.getElementById('misskey_meta');
 
 let cachedMeta = miLocalStorage.getItem('instance') ? JSON.parse(miLocalStorage.getItem('instance')!) : null;
 let cachedAt = miLocalStorage.getItem('instanceCachedAt') ? parseInt(miLocalStorage.getItem('instanceCachedAt')!) : 0;
-const providedMeta = providedMetaEl && providedMetaEl.textContent ? JSON.parse(providedMetaEl.textContent) : null;
+const providedMeta: Misskey.entities.MetaDetailed | null = providedMetaEl && providedMetaEl.textContent ? JSON.parse(providedMetaEl.textContent) : null;
 const providedAt = providedMetaEl && providedMetaEl.dataset.generatedAt ? parseInt(providedMetaEl.dataset.generatedAt) : 0;
 if (providedAt > cachedAt) {
 	miLocalStorage.setItem('instance', JSON.stringify(providedMeta));
@@ -38,6 +38,19 @@ export const notFoundImageUrl = computed(() => instance.notFoundImageUrl ?? DEFA
 
 export const isEnabledUrlPreview = computed(() => instance.enableUrlPreview ?? true);
 
+/** instanceの中身が入っていることを保証する */
+export async function initInstance() {
+	if (instance == null || Object.keys(instance).length === 0) {
+		if (providedMeta != null) {
+			for (const [k, v] of Object.entries(providedMeta)) {
+				instance[k] = v;
+			}
+		} else {
+			await fetchInstance(true);
+		}
+	}
+}
+
 export async function fetchInstance(force = false): Promise<Misskey.entities.MetaDetailed> {
 	if (!force) {
 		const cachedAt = miLocalStorage.getItem('instanceCachedAt') ? parseInt(miLocalStorage.getItem('instanceCachedAt')!) : 0;
@@ -60,3 +73,9 @@ export async function fetchInstance(force = false): Promise<Misskey.entities.Met
 
 	return instance;
 }
+
+/** キャッシュだけ飛ばす（リロード後からは新しい設定を読み込む） */
+export function pruneInstanceCache() {
+	miLocalStorage.removeItem('instance');
+	miLocalStorage.removeItem('instanceCachedAt');
+}
diff --git a/packages/frontend/src/pages/admin/client-setting-overrides.vue b/packages/frontend/src/pages/admin/client-setting-overrides.vue
new file mode 100644
index 0000000000..16eab515f9
--- /dev/null
+++ b/packages/frontend/src/pages/admin/client-setting-overrides.vue
@@ -0,0 +1,261 @@
+<!--
+SPDX-FileCopyrightText: syuilo and misskey-project
+SPDX-License-Identifier: AGPL-3.0-only
+-->
+
+<template>
+<div>
+	<MkStickyContainer>
+		<template #header><XHeader :tabs="headerTabs"/></template>
+		<MkSpacer :contentMax="700" :marginMin="16" :marginMax="32">
+			<div class="_gaps">
+				<MkInfo warn :class="$style.warn">{{ i18n.ts.clientSettingOverridesWarn }}</MkInfo>
+				<div v-if="fetching">
+					<MkLoading/>
+				</div>
+				<div v-else class="_gaps_s">
+					<MkInput v-model="query" type="search">
+						<template #prefix><i class="ti ti-search"></i></template>
+					</MkInput>
+
+					<MkFolder
+						v-for="def, key in clientSettingOverrides"
+						:key="key"
+						v-show="query === '' || key.toLowerCase().includes(query.toLowerCase())"
+					>
+						<template #label>{{ key }}</template>
+						<template #suffix>
+							<span v-if="def.enableOverride && def.overrideValue != null && def.overrideValue !== def.defaultValue" class="_warn">{{ i18n.ts.modified }}</span>
+						</template>
+						<div class="_gaps">
+							<MkKeyValue>
+								<template #key>{{ i18n.ts.default }}</template>
+								<template #value>
+									<MkCode v-bind="getMkCodeProps(def)"></MkCode>
+								</template>
+							</MkKeyValue>
+							<MkSwitch v-model="def.enableOverride">{{ i18n.ts.enableOverride }}</MkSwitch>
+							<MkInput v-if="def.formType === 'text'" v-model="def.overrideValue" :disabled="!def.enableOverride" type="text">
+								<template #label>{{ i18n.ts.overrideValue }}</template>
+							</MkInput>
+							<MkInput v-else-if="def.formType === 'number'" v-model="def.overrideValue" :disabled="!def.enableOverride" type="number">
+								<template #label>{{ i18n.ts.overrideValue }}</template>
+							</MkInput>
+							<MkSwitch v-else-if="def.formType === 'boolean'" v-model="def.overrideValue" :disabled="!def.enableOverride">
+								<template #label>{{ i18n.ts.overrideValue }}</template>
+								<template #caption>{{ i18n.ts.onToTrue }}</template>
+							</MkSwitch>
+							<MkTextarea v-else-if="def.formType === 'codeEditor'" v-model="def.overrideValue" :disabled="!def.enableOverride" pre>
+								<template #label>{{ i18n.ts.overrideValue }}</template>
+							</MkTextarea>
+						</div>
+					</MkFolder>
+				</div>
+			</div>
+		</MkSpacer>
+		<template #footer>
+			<div :class="$style.footer">
+				<div :class="$style.footerInner">
+					<div class="_buttons">
+						<MkButton primary @click="save"><i class="ti ti-check"></i> {{ i18n.ts.save }}</MkButton>
+						<MkButton danger @click="reset"><i class="ti ti-trash"></i> {{ i18n.ts.reset }}</MkButton>
+					</div>
+				</div>
+			</div>
+		</template>
+	</MkStickyContainer>
+</div>
+</template>
+
+<script lang="ts" setup>
+import { ref, computed } from 'vue';
+import XHeader from './_header_.vue';
+import * as os from '@/os.js';
+import { ColdDeviceStorage, defaultStore } from '@/store.js';
+import { pruneInstanceCache } from '@/instance.js';
+import { i18n } from '@/i18n.js';
+import { definePageMetadata } from '@/scripts/page-metadata.js';
+import MkInfo from '@/components/MkInfo.vue';
+import MkButton from '@/components/MkButton.vue';
+import MkInput from '@/components/MkInput.vue';
+import MkFolder from '@/components/MkFolder.vue';
+import MkKeyValue from '@/components/MkKeyValue.vue';
+import MkCode from '@/components/MkCode.vue';
+import { misskeyApi } from '@/scripts/misskey-api.js';
+import { reloadAsk } from '@/scripts/reload-ask.js';
+import MkSwitch from '@/components/MkSwitch.vue';
+import MkTextarea from '@/components/MkTextarea.vue';
+
+const query = ref('');
+
+const notConfigurableDefaultStoreSettings = [
+	'accountSetupWizard',
+	'timelineTutorials',
+	'abusesTutorial',
+	'memo',
+	'mutedAds',
+	'statusbars',
+	'widgets',
+	'pinnedUserLists',
+	'recentlyUsedEmojis',
+	'recentlyUsedUsers',
+	'forceShowAds',
+	'additionalUnicodeEmojiIndexes',
+	'themeInitial',
+] satisfies (keyof typeof defaultStore.def)[];
+
+const notConfigurableColdDeviceStorageSettings = [
+	'darkTheme',
+	'lightTheme',
+	'plugins',
+] satisfies (keyof typeof ColdDeviceStorage.default)[];
+
+type ClientSettingOverridesUIDefObj = {
+	formType: 'text' | 'number' | 'boolean' | 'codeEditor';
+	enableOverride: boolean;
+	defaultValue: any;
+	overrideValue?: any;
+}
+
+const fetching = ref(true);
+const clientSettingOverrides = ref<Record<string, ClientSettingOverridesUIDefObj>>();
+
+function getMkCodeProps(def: ClientSettingOverridesUIDefObj) {
+	if (typeof def.defaultValue === 'string') {
+		return {
+			code: def.defaultValue,
+			forceShow: true,
+		};
+	} else {
+		return {
+			code: JSON.stringify(def.defaultValue, null, 4),
+			lang: 'json',
+			forceShow: true,
+		};
+	}
+}
+
+function typeSafeObjectEntries<T extends Record<string, any>>(obj: T) {
+	return Object.entries(obj) as [keyof T, T[keyof T]][];
+}
+
+function getClientSettingOverridesUIDefObj(def: unknown): ClientSettingOverridesUIDefObj {
+	return {
+		formType: (() => {
+			if (typeof def === 'boolean') {
+				return 'boolean';
+			} else if (typeof def === 'number') {
+				return 'number';
+			} else if (typeof def === 'object') {
+				return 'codeEditor';
+			} else {
+				return 'text';
+			}
+		})() satisfies ClientSettingOverridesUIDefObj['formType'] as ClientSettingOverridesUIDefObj['formType'],
+		enableOverride: false,
+		defaultValue: def,
+		overrideValue: def,
+	};
+}
+
+async function fetch() {
+	fetching.value = true;
+	const overrideDefs = Object.fromEntries([
+		...typeSafeObjectEntries(defaultStore.def)
+			.filter(([key, _]) => !(notConfigurableDefaultStoreSettings as string[]).includes(key))
+			.map(([key, def]) => [`defaultStore::${key}`, getClientSettingOverridesUIDefObj(def.default)]),
+		...typeSafeObjectEntries(ColdDeviceStorage.default)
+			.filter(([key, _]) => !(notConfigurableColdDeviceStorageSettings as string[]).includes(key))
+			.map(([key, def]) => [`ColdDeviceStorage::${key}`, getClientSettingOverridesUIDefObj(def)]),
+	]);
+	const res = await misskeyApi('admin/meta');
+	if (res.defaultClientSettingOverrides != null) {
+		try {
+			const parsed = JSON.parse(res.defaultClientSettingOverrides);
+			for (const key in parsed) {
+				if (key in overrideDefs) {
+					overrideDefs[key].enableOverride = true;
+					overrideDefs[key].overrideValue = parsed[key];
+				}
+			}
+		} catch (e) {
+			console.error(e);
+		}
+	}
+
+	clientSettingOverrides.value = overrideDefs;
+	fetching.value = false;
+}
+
+async function save() {
+	if (clientSettingOverrides.value == null) return;
+
+	const overrides = Object.fromEntries(
+		typeSafeObjectEntries(clientSettingOverrides.value)
+			.filter(([key, def]) => (
+				def.enableOverride &&
+				def.overrideValue !== def.defaultValue &&
+				JSON.stringify(def.overrideValue) !== JSON.stringify(def.defaultValue)
+			))
+			.map(([key, def]) => [key, def.overrideValue])
+	);
+
+	let defaultClientSettingOverrides: string | null = JSON.stringify(overrides);
+
+	if (Object.keys(overrides).length === 0) {
+		defaultClientSettingOverrides = null;
+	}
+
+	await os.apiWithDialog('admin/update-meta', {
+		defaultClientSettingOverrides,
+	});
+
+	await fetch();
+	pruneInstanceCache();
+	await reloadAsk({ reason: i18n.ts.reloadToApplySetting });
+}
+
+async function reset() {
+	const { canceled } = await os.confirm({
+		type: 'warning',
+		text: i18n.ts.resetAreYouSure,
+	});
+
+	if (canceled) return;
+
+	await os.apiWithDialog('admin/update-meta', {
+		defaultClientSettingOverrides: null,
+	});
+
+	await fetch();
+}
+
+fetch();
+
+const headerActions = computed(() => []);
+
+const headerTabs = computed(() => []);
+
+definePageMetadata(() => ({
+	title: i18n.ts.clientSettingOverrides,
+	icon: 'ti ti-checkbox',
+}));
+</script>
+
+<style lang="scss" module>
+.warn {
+	white-space: pre-wrap;
+}
+
+.footer {
+	backdrop-filter: var(--MI-blur, blur(15px));
+	background: var(--MI_THEME-acrylicBg);
+	border-top: solid .5px var(--MI_THEME-divider);
+}
+
+.footerInner {
+	max-width: 700px;
+	margin: 0 auto;
+	padding: 16px;
+}
+</style>
diff --git a/packages/frontend/src/pages/admin/settings.vue b/packages/frontend/src/pages/admin/settings.vue
index ea7603a45a..689b7aa165 100644
--- a/packages/frontend/src/pages/admin/settings.vue
+++ b/packages/frontend/src/pages/admin/settings.vue
@@ -249,6 +249,8 @@ SPDX-License-Identifier: AGPL-3.0-only
 						<MkButton primary @click="chooseProxyAccount">{{ i18n.ts.selectAccount }}</MkButton>
 					</div>
 				</MkFolder>
+
+				<FormLink to="/admin/client-setting-overrides">{{ i18n.ts.clientSettingOverrides }} <span class="_beta">{{ i18n.ts.beta }}</span></FormLink>
 			</div>
 		</MkSpacer>
 	</MkStickyContainer>
@@ -274,6 +276,7 @@ import MkKeyValue from '@/components/MkKeyValue.vue';
 import { useForm } from '@/scripts/use-form.js';
 import MkFormFooter from '@/components/MkFormFooter.vue';
 import MkRadios from '@/components/MkRadios.vue';
+import FormLink from '@/components/form/link.vue';
 
 const meta = await misskeyApi('admin/meta');
 
diff --git a/packages/frontend/src/pizzax.ts b/packages/frontend/src/pizzax.ts
index ac325e923f..b54203dc9d 100644
--- a/packages/frontend/src/pizzax.ts
+++ b/packages/frontend/src/pizzax.ts
@@ -13,7 +13,7 @@ import { get, set } from '@/scripts/idb-proxy.js';
 import { defaultStore } from '@/store.js';
 import { useStream } from '@/stream.js';
 import { deepClone } from '@/scripts/clone.js';
-import { deepMerge } from '@/scripts/merge.js';
+import { deepMerge, type DeepPartial } from '@/scripts/merge.js';
 
 type StateDef = Record<string, {
 	where: 'account' | 'device' | 'deviceAccount';
@@ -44,6 +44,7 @@ export class Storage<T extends StateDef> {
 	public readonly def: T;
 
 	// TODO: これが実装されたらreadonlyにしたい: https://github.com/microsoft/TypeScript/issues/37487
+	private readonly defaultState: State<T>;
 	public readonly state: State<T>;
 	public readonly reactiveState: ReactiveState<T>;
 
@@ -60,7 +61,7 @@ export class Storage<T extends StateDef> {
 		return promise;
 	}
 
-	constructor(key: string, def: T) {
+	constructor(key: string, def: T, defaultOverrides?: DeepPartial<State<T>>) {
 		this.key = key;
 		this.deviceStateKeyName = `pizzax::${key}`;
 		this.deviceAccountStateKeyName = $i ? `pizzax::${key}::${$i.id}` : '';
@@ -69,25 +70,43 @@ export class Storage<T extends StateDef> {
 
 		this.pizzaxChannel = new BroadcastChannel(`pizzax::${key}`);
 
+		this.defaultState = {} as State<T>;
 		this.state = {} as State<T>;
 		this.reactiveState = {} as ReactiveState<T>;
 
 		for (const [k, v] of Object.entries(def) as [keyof T, T[keyof T]['default']][]) {
-			this.state[k] = v.default;
-			this.reactiveState[k] = ref(v.default);
+			let _defaultState = v.default;
+			if (
+				defaultOverrides != null &&
+				this.isPureObject(defaultOverrides) &&
+				defaultOverrides[k] !== undefined // ←意図的にnullになっている可能性があるためundefined判定
+			) {
+				if (this.isPureObject(defaultOverrides[k]) && this.isPureObject(v.default)) {
+					_defaultState = deepMerge(defaultOverrides[k], v.default);
+				} else if (Array.isArray(defaultOverrides[k]) && Array.isArray(v.default)) {
+					_defaultState = Array.from(new Set([...defaultOverrides[k], ...v.default]));
+				} else {
+					_defaultState = defaultOverrides[k];
+				}
+				if (_DEV_) console.log('defaultState', k, _defaultState);
+			}
+
+			this.defaultState[k] = _defaultState;
+			this.state[k] = _defaultState;
+			this.reactiveState[k] = ref(_defaultState);
 		}
 
 		this.ready = this.init();
 		this.loaded = this.ready.then(() => this.load());
 	}
 
-	private isPureObject(value: unknown): value is Record<string | number | symbol, unknown> {
+	private isPureObject(value: unknown): value is Record<PropertyKey, unknown> {
 		return typeof value === 'object' && value !== null && !Array.isArray(value);
 	}
 
 	private mergeState<X>(value: X, def: X): X {
 		if (this.isPureObject(value) && this.isPureObject(def)) {
-			const merged = deepMerge(value, def);
+			const merged = deepMerge(value as DeepPartial<X>, def);
 
 			if (_DEV_) console.log('Merging state. Incoming: ', value, ' Default: ', def, ' Result: ', merged);
 
@@ -105,14 +124,14 @@ export class Storage<T extends StateDef> {
 
 		for (const [k, v] of Object.entries(this.def) as [keyof T, T[keyof T]['default']][]) {
 			if (v.where === 'device' && Object.prototype.hasOwnProperty.call(deviceState, k)) {
-				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(deviceState[k], v.default);
+				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(deviceState[k], this.defaultState[k]);
 			} else if (v.where === 'account' && $i && Object.prototype.hasOwnProperty.call(registryCache, k)) {
-				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(registryCache[k], v.default);
+				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(registryCache[k], this.defaultState[k]);
 			} else if (v.where === 'deviceAccount' && Object.prototype.hasOwnProperty.call(deviceAccountState, k)) {
-				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(deviceAccountState[k], v.default);
+				this.reactiveState[k].value = this.state[k] = this.mergeState<T[keyof T]['default']>(deviceAccountState[k], this.defaultState[k]);
 			} else {
-				this.reactiveState[k].value = this.state[k] = v.default;
-				if (_DEV_) console.log('Use default value', k, v.default);
+				this.reactiveState[k].value = this.state[k] = this.defaultState[k];
+				if (_DEV_) console.log('Use default value', k, this.defaultState[k]);
 			}
 		}
 
diff --git a/packages/frontend/src/router/definition.ts b/packages/frontend/src/router/definition.ts
index e98e0b59b1..ea2cfdc6b3 100644
--- a/packages/frontend/src/router/definition.ts
+++ b/packages/frontend/src/router/definition.ts
@@ -486,6 +486,10 @@ const routes: RouteDef[] = [{
 		path: '/system-webhook',
 		name: 'system-webhook',
 		component: page(() => import('@/pages/admin/system-webhook.vue')),
+	}, {
+		path: '/client-setting-overrides',
+		name: 'client-setting-overrides',
+		component: page(() => import('@/pages/admin/client-setting-overrides.vue')),
 	}, {
 		path: '/',
 		component: page(() => import('@/pages/_empty_.vue')),
diff --git a/packages/frontend/src/scripts/merge.ts b/packages/frontend/src/scripts/merge.ts
index 9794a300da..004b6d42a4 100644
--- a/packages/frontend/src/scripts/merge.ts
+++ b/packages/frontend/src/scripts/merge.ts
@@ -7,10 +7,10 @@ import { deepClone } from './clone.js';
 import type { Cloneable } from './clone.js';
 
 export type DeepPartial<T> = {
-	[P in keyof T]?: T[P] extends Record<string | number | symbol, unknown> ? DeepPartial<T[P]> : T[P];
+	[P in keyof T]?: T[P] extends Record<PropertyKey, unknown> ? DeepPartial<T[P]> : T[P];
 };
 
-function isPureObject(value: unknown): value is Record<string | number | symbol, unknown> {
+function isPureObject(value: unknown): value is Record<PropertyKey, unknown> {
 	return typeof value === 'object' && value !== null && !Array.isArray(value);
 }
 
@@ -18,14 +18,14 @@ function isPureObject(value: unknown): value is Record<string | number | symbol,
  * valueにないキーをdefからもらう（再帰的）\
  * nullはそのまま、undefinedはdefの値
  **/
-export function deepMerge<X extends Record<string | number | symbol, unknown>>(value: DeepPartial<X>, def: X): X {
+export function deepMerge<X extends Record<PropertyKey, unknown>>(value: DeepPartial<X>, def: X): X {
 	if (isPureObject(value) && isPureObject(def)) {
 		const result = deepClone(value as Cloneable) as X;
 		for (const [k, v] of Object.entries(def) as [keyof X, X[keyof X]][]) {
 			if (!Object.prototype.hasOwnProperty.call(value, k) || value[k] === undefined) {
 				result[k] = v;
 			} else if (isPureObject(v) && isPureObject(result[k])) {
-				const child = deepClone(result[k] as Cloneable) as DeepPartial<X[keyof X] & Record<string | number | symbol, unknown>>;
+				const child = deepClone(result[k] as Cloneable) as DeepPartial<X[keyof X] & Record<PropertyKey, unknown>>;
 				result[k] = deepMerge<typeof v>(child, v);
 			}
 		}
diff --git a/packages/frontend/src/scripts/reload-ask.ts b/packages/frontend/src/scripts/reload-ask.ts
index 733d91b85a..0e82cb06d8 100644
--- a/packages/frontend/src/scripts/reload-ask.ts
+++ b/packages/frontend/src/scripts/reload-ask.ts
@@ -12,7 +12,7 @@ let isReloadConfirming = false;
 export async function reloadAsk(opts: {
 	unison?: boolean;
 	reason?: string;
-}) {
+} = {}) {
 	if (isReloadConfirming) {
 		return;
 	}
diff --git a/packages/frontend/src/scripts/store-overrides.ts b/packages/frontend/src/scripts/store-overrides.ts
new file mode 100644
index 0000000000..9dcba56e48
--- /dev/null
+++ b/packages/frontend/src/scripts/store-overrides.ts
@@ -0,0 +1,33 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { initInstance, instance } from '@/instance.js';
+
+export async function getDefaultStoreOverrides() {
+	await initInstance();
+	if (instance.defaultClientSettingOverrides != null) {
+		try {
+			const clientSettingOverrides = JSON.parse(instance.defaultClientSettingOverrides);
+			const out = Object.fromEntries(Object.keys(clientSettingOverrides).filter(key => key.startsWith('defaultStore::')).map(key => [key.split('::')[1], clientSettingOverrides[key]]));
+			return out;
+		} catch (err) {
+			return null;
+		}
+	}
+	return null;
+}
+
+export function getColdDeviceStorageOverrides() {
+	if (instance.defaultClientSettingOverrides != null) {
+		try {
+			const clientSettingOverrides = JSON.parse(instance.defaultClientSettingOverrides);
+			const out = Object.fromEntries(Object.keys(clientSettingOverrides).filter(key => key.startsWith('ColdDeviceStorage::')).map(key => [key.split('::')[1], clientSettingOverrides[key]]));
+			return out;
+		} catch (err) {
+			return null;
+		}
+	}
+	return null;
+}
diff --git a/packages/frontend/src/store.ts b/packages/frontend/src/store.ts
index 911a463636..78328992ab 100644
--- a/packages/frontend/src/store.ts
+++ b/packages/frontend/src/store.ts
@@ -12,6 +12,7 @@ import { miLocalStorage } from './local-storage.js';
 import type { SoundType } from '@/scripts/sound.js';
 import { Storage } from '@/pizzax.js';
 import type { Ast } from '@syuilo/aiscript';
+import { getColdDeviceStorageOverrides, getDefaultStoreOverrides } from '@/scripts/store-overrides.js';
 
 interface PostFormAction {
 	title: string,
@@ -502,7 +503,7 @@ export const defaultStore = markRaw(new Storage('base', {
 		where: 'device',
 		default: { type: 'syuilo/bubble2', volume: 1 } as SoundStore,
 	},
-}));
+}, await getDefaultStoreOverrides() ?? undefined));
 
 // TODO: 他のタブと永続化されたstateを同期
 
@@ -548,7 +549,8 @@ export class ColdDeviceStorage {
 		//       (indexedDBはnullを保存できるため、ユーザーが意図してnullを格納した可能性がある)
 		const value = miLocalStorage.getItem(`${PREFIX}${key}`);
 		if (value == null) {
-			return ColdDeviceStorage.default[key];
+			const override = getColdDeviceStorageOverrides();
+			return override != null ? override[key] ?? ColdDeviceStorage.default[key] : ColdDeviceStorage.default[key];
 		} else {
 			return JSON.parse(value);
 		}
diff --git a/packages/misskey-js/src/autogen/types.ts b/packages/misskey-js/src/autogen/types.ts
index a5333d4f93..48da4cec98 100644
--- a/packages/misskey-js/src/autogen/types.ts
+++ b/packages/misskey-js/src/autogen/types.ts
@@ -5035,6 +5035,7 @@ export type components = {
         /** @default true */
         miauth?: boolean;
       };
+      defaultClientSettingOverrides: string | null;
       proxyAccountName: string | null;
       /** @example false */
       requireSetup: boolean;
@@ -5186,6 +5187,7 @@ export type operations = {
             deeplIsPro: boolean;
             defaultDarkTheme: string | null;
             defaultLightTheme: string | null;
+            defaultClientSettingOverrides: string | null;
             description: string | null;
             disableRegistration: boolean;
             impressumUrl: string | null;
@@ -9496,6 +9498,7 @@ export type operations = {
           description?: string | null;
           defaultLightTheme?: string | null;
           defaultDarkTheme?: string | null;
+          defaultClientSettingOverrides?: string | null;
           cacheRemoteFiles?: boolean;
           cacheRemoteSensitiveFiles?: boolean;
           emailRequiredForSignup?: boolean;