diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0461fc832..426727104 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@
 - Fix: カスタム絵文字管理画面(beta)にてisSensitive/localOnlyの絞り込みが上手くいかない問題の修正 ( #15445 )
 - Fix: ユーザのサジェスト中に@を入力してもサジェスト結果が消えないように `#14385`
 - Fix: CWの注釈が100文字を超えている場合、ノート投稿ボタンを非アクティブに
+- Fix: テーマ選択で現在のテーマが初期表示されていない問題を修正
 - 翻訳の更新
 
 ### Server
diff --git a/packages/frontend/src/components/MkSelect.vue b/packages/frontend/src/components/MkSelect.vue
index 83a79d0c9..15717802e 100644
--- a/packages/frontend/src/components/MkSelect.vue
+++ b/packages/frontend/src/components/MkSelect.vue
@@ -41,11 +41,28 @@ SPDX-License-Identifier: AGPL-3.0-only
 
 <script lang="ts" setup>
 import { onMounted, nextTick, ref, watch, computed, toRefs, useSlots } from 'vue';
-import type { VNode, VNodeChild } from 'vue';
 import { useInterval } from '@@/js/use-interval.js';
+import type { VNode, VNodeChild } from 'vue';
 import type { MenuItem } from '@/types/menu.js';
 import * as os from '@/os.js';
 
+type ItemOption = {
+	type?: 'option';
+	value: string | number | null;
+	label: string;
+};
+
+type ItemGroup = {
+	type: 'group';
+	label: string;
+	items: ItemOption[];
+};
+
+export type MkSelectItem = ItemOption | ItemGroup;
+
+// TODO: itemsをslot内のoptionで指定する用法は廃止する(props.itemsを必須化する)
+// see: https://github.com/misskey-dev/misskey/issues/15558
+
 const props = defineProps<{
 	modelValue: string | number | null;
 	required?: boolean;
@@ -56,6 +73,7 @@ const props = defineProps<{
 	inline?: boolean;
 	small?: boolean;
 	large?: boolean;
+	items?: MkSelectItem[];
 }>();
 
 const emit = defineEmits<{
@@ -107,7 +125,30 @@ onMounted(() => {
 	});
 });
 
-watch(modelValue, () => {
+watch([modelValue, () => props.items], () => {
+	if (props.items) {
+		let found: ItemOption | null = null;
+		for (const item of props.items) {
+			if (item.type === 'group') {
+				for (const option of item.items) {
+					if (option.value === modelValue.value) {
+						found = option;
+						break;
+					}
+				}
+			} else {
+				if (item.value === modelValue.value) {
+					found = item;
+					break;
+				}
+			}
+		}
+		if (found) {
+			currentValueText.value = found.label;
+		}
+		return;
+	}
+
 	const scanOptions = (options: VNodeChild[]) => {
 		for (const vnode of options) {
 			if (typeof vnode !== 'object' || vnode === null || Array.isArray(vnode)) continue;
@@ -130,7 +171,7 @@ watch(modelValue, () => {
 	};
 
 	scanOptions(slots.default!());
-}, { immediate: true });
+}, { immediate: true, deep: true });
 
 function show() {
 	if (opening.value) return;
@@ -139,41 +180,70 @@ function show() {
 	opening.value = true;
 
 	const menu: MenuItem[] = [];
-	let options = slots.default!();
 
-	const pushOption = (option: VNode) => {
-		menu.push({
-			text: option.children as string,
-			active: computed(() => modelValue.value === option.props?.value),
-			action: () => {
-				emit('update:modelValue', option.props?.value);
-			},
-		});
-	};
-
-	const scanOptions = (options: VNodeChild[]) => {
-		for (const vnode of options) {
-			if (typeof vnode !== 'object' || vnode === null || Array.isArray(vnode)) continue;
-			if (vnode.type === 'optgroup') {
-				const optgroup = vnode;
+	if (props.items) {
+		for (const item of props.items) {
+			if (item.type === 'group') {
 				menu.push({
 					type: 'label',
-					text: optgroup.props?.label,
+					text: item.label,
 				});
-				if (Array.isArray(optgroup.children)) scanOptions(optgroup.children);
-			} else if (Array.isArray(vnode.children)) { // 何故かフラグメントになってくることがある
-				const fragment = vnode;
-				if (Array.isArray(fragment.children)) scanOptions(fragment.children);
-			} else if (vnode.props == null) { // v-if で条件が false のときにこうなる
-				// nop?
+				for (const option of item.items) {
+					menu.push({
+						text: option.label,
+						active: computed(() => modelValue.value === option.value),
+						action: () => {
+							emit('update:modelValue', option.value);
+						},
+					});
+				}
 			} else {
-				const option = vnode;
-				pushOption(option);
+				menu.push({
+					text: item.label,
+					active: computed(() => modelValue.value === item.value),
+					action: () => {
+						emit('update:modelValue', item.value);
+					},
+				});
 			}
 		}
-	};
+	} else {
+		let options = slots.default!();
 
-	scanOptions(options);
+		const pushOption = (option: VNode) => {
+			menu.push({
+				text: option.children as string,
+				active: computed(() => modelValue.value === option.props?.value),
+				action: () => {
+					emit('update:modelValue', option.props?.value);
+				},
+			});
+		};
+
+		const scanOptions = (options: VNodeChild[]) => {
+			for (const vnode of options) {
+				if (typeof vnode !== 'object' || vnode === null || Array.isArray(vnode)) continue;
+				if (vnode.type === 'optgroup') {
+					const optgroup = vnode;
+					menu.push({
+						type: 'label',
+						text: optgroup.props?.label,
+					});
+					if (Array.isArray(optgroup.children)) scanOptions(optgroup.children);
+				} else if (Array.isArray(vnode.children)) { // 何故かフラグメントになってくることがある
+					const fragment = vnode;
+					if (Array.isArray(fragment.children)) scanOptions(fragment.children);
+				} else if (vnode.props == null) { // v-if で条件が false のときにこうなる
+					// nop?
+				} else {
+					const option = vnode;
+					pushOption(option);
+				}
+			}
+		};
+
+		scanOptions(options);
+	}
 
 	os.popupMenu(menu, container.value, {
 		width: container.value?.offsetWidth,
diff --git a/packages/frontend/src/pages/settings/theme.vue b/packages/frontend/src/pages/settings/theme.vue
index f1ec23158..fcf5b3cd9 100644
--- a/packages/frontend/src/pages/settings/theme.vue
+++ b/packages/frontend/src/pages/settings/theme.vue
@@ -32,27 +32,13 @@ SPDX-License-Identifier: AGPL-3.0-only
 	</div>
 
 	<div class="selects">
-		<MkSelect v-model="lightThemeId" large class="select">
+		<MkSelect v-model="lightThemeId" large class="select" :items="lightThemeSelectorItems">
 			<template #label>{{ i18n.ts.themeForLightMode }}</template>
 			<template #prefix><i class="ti ti-sun"></i></template>
-			<option v-if="instanceLightTheme" :key="'instance:' + instanceLightTheme.id" :value="instanceLightTheme.id">{{ instanceLightTheme.name }}</option>
-			<optgroup v-if="installedLightThemes.length > 0" :label="i18n.ts._theme.installedThemes">
-				<option v-for="x in installedLightThemes" :key="'installed:' + x.id" :value="x.id">{{ x.name }}</option>
-			</optgroup>
-			<optgroup :label="i18n.ts._theme.builtinThemes">
-				<option v-for="x in builtinLightThemes" :key="'builtin:' + x.id" :value="x.id">{{ x.name }}</option>
-			</optgroup>
 		</MkSelect>
-		<MkSelect v-model="darkThemeId" large class="select">
+		<MkSelect v-model="darkThemeId" large class="select" :items="darkThemeSelectorItems">
 			<template #label>{{ i18n.ts.themeForDarkMode }}</template>
 			<template #prefix><i class="ti ti-moon"></i></template>
-			<option v-if="instanceDarkTheme" :key="'instance:' + instanceDarkTheme.id" :value="instanceDarkTheme.id">{{ instanceDarkTheme.name }}</option>
-			<optgroup v-if="installedDarkThemes.length > 0" :label="i18n.ts._theme.installedThemes">
-				<option v-for="x in installedDarkThemes" :key="'installed:' + x.id" :value="x.id">{{ x.name }}</option>
-			</optgroup>
-			<optgroup :label="i18n.ts._theme.builtinThemes">
-				<option v-for="x in builtinDarkThemes" :key="'builtin:' + x.id" :value="x.id">{{ x.name }}</option>
-			</optgroup>
 		</MkSelect>
 	</div>
 
@@ -73,6 +59,7 @@ SPDX-License-Identifier: AGPL-3.0-only
 <script lang="ts" setup>
 import { computed, onActivated, ref, watch } from 'vue';
 import JSON5 from 'json5';
+import type { MkSelectItem } from '@/components/MkSelect.vue';
 import MkSwitch from '@/components/MkSwitch.vue';
 import MkSelect from '@/components/MkSelect.vue';
 import FormSection from '@/components/form/section.vue';
@@ -102,6 +89,70 @@ const installedLightThemes = computed(() => installedThemes.value.filter(t => t.
 const builtinLightThemes = computed(() => builtinThemes.value.filter(t => t.base === 'light' || t.kind === 'light'));
 const themes = computed(() => uniqueBy([instanceDarkTheme.value, instanceLightTheme.value, ...builtinThemes.value, ...installedThemes.value].filter(x => x != null), theme => theme.id));
 
+const lightThemeSelectorItems = computed(() => {
+	const items = [] as MkSelectItem[];
+	if (instanceLightTheme.value) {
+		items.push({
+			type: 'option',
+			value: instanceLightTheme.value.id,
+			label: instanceLightTheme.value.name,
+		});
+	}
+	if (installedLightThemes.value.length > 0) {
+		items.push({
+			type: 'group',
+			label: i18n.ts._theme.installedThemes,
+			items: installedLightThemes.value.map(x => ({
+				type: 'option',
+				value: x.id,
+				label: x.name,
+			})),
+		});
+	}
+	items.push({
+		type: 'group',
+		label: i18n.ts._theme.builtinThemes,
+		items: builtinLightThemes.value.map(x => ({
+			type: 'option',
+			value: x.id,
+			label: x.name,
+		})),
+	});
+	return items;
+});
+
+const darkThemeSelectorItems = computed(() => {
+	const items = [] as MkSelectItem[];
+	if (instanceDarkTheme.value) {
+		items.push({
+			type: 'option',
+			value: instanceDarkTheme.value.id,
+			label: instanceDarkTheme.value.name,
+		});
+	}
+	if (installedDarkThemes.value.length > 0) {
+		items.push({
+			type: 'group',
+			label: i18n.ts._theme.installedThemes,
+			items: installedDarkThemes.value.map(x => ({
+				type: 'option',
+				value: x.id,
+				label: x.name,
+			})),
+		});
+	}
+	items.push({
+		type: 'group',
+		label: i18n.ts._theme.builtinThemes,
+		items: builtinDarkThemes.value.map(x => ({
+			type: 'option',
+			value: x.id,
+			label: x.name,
+		})),
+	});
+	return items;
+});
+
 const darkTheme = ColdDeviceStorage.ref('darkTheme');
 const darkThemeId = computed({
 	get() {