diff --git a/src/models/note.ts b/src/models/note.ts
index 8ca65bb42..9945ee42a 100644
--- a/src/models/note.ts
+++ b/src/models/note.ts
@@ -377,15 +377,40 @@ export const pack = async (
 	}
 	//#endregion
 
-	if (_note.user.isCat && _note.text) {
-		_note.text = (_note.text
-			// ja-JP
-			.replace(/な/g, 'にゃ').replace(/ナ/g, 'ニャ').replace(/ﾅ/g, 'ﾆｬ')
-			// ko-KR
-			.replace(/[나-낳]/g, (match: string) => String.fromCharCode(
-				match.codePointAt(0)  + '냐'.charCodeAt(0) - '나'.charCodeAt(0)
-			))
-		);
+	const nyamap: { [x: string]: string } = {
+	//#region nyanize: ja-JP
+		'な': 'にゃ',
+		'ナ': 'ニャ',
+		'ﾅ': 'ﾆｬ'
+	//#endregion
+	};
+
+	//#region nyanize: ko-KR
+	const diffKoKr = '냐'.charCodeAt(0) - '나'.charCodeAt(0);
+	for (let i = '나'.charCodeAt(0); i <= '낳'.charCodeAt(0); i++)
+		nyamap[String.fromCharCode(i)] = String.fromCharCode(i + diffKoKr);
+	//#endregion
+
+	const raw: string = _note.text;
+	const stack = [!!_note.user.isCat];
+	for (let i = 0; i < raw.length; i++) {
+		const head = raw[i];
+
+		if (head === '<') {
+			const [, tag, state] = raw.slice(i).match(/^<((\/?!?)nya>)/i) || [, , , ];
+
+			if (typeof state === 'string') {
+				if (state[0] === '/')
+					stack.shift();
+				else
+					stack.unshift(!state);
+
+				i += tag.length;
+				continue;
+			}
+		}
+
+		_note.text += stack[0] && nyamap[head] || head;
 	}
 
 	if (!opts.skipHide) {
diff --git a/src/services/note/create.ts b/src/services/note/create.ts
index d3c8699b2..c6c72269e 100644
--- a/src/services/note/create.ts
+++ b/src/services/note/create.ts
@@ -147,6 +147,17 @@ export default async (user: IUser, data: Option, silent = false) => new Promise<
 
 	if (data.text) {
 		data.text = data.text.trim();
+
+		const stack: string[] = [];
+		for (const tag of [...data.text.match(/<\/?!?nya>/ig)]
+			.map(x => x.toLocaleLowerCase()))
+				if (tag.includes('/')) {
+					if (stack.pop() !== tag.replace('/', ''))
+						return rej('Invalid nyanize syntax');
+				} else
+					stack.push(tag);
+		if (stack.length)
+			return rej('Invalid nyanize syntax');
 	}
 
 	let tags = data.apHashtags;
@@ -155,10 +166,11 @@ export default async (user: IUser, data: Option, silent = false) => new Promise<
 
 	// Parse MFM if needed
 	if (!tags || !emojis || !mentionedUsers) {
-		const tokens = data.text ? parse(data.text) : [];
+		const text = data.text && data.text.replace(/^<\/?!?nya>/ig, '');
+		const tokens = text ? parse(text) : [];
 		const cwTokens = data.cw ? parse(data.cw) : [];
 		const choiceTokens = data.poll && data.poll.choices
-			? concat((data.poll.choices as IChoice[]).map(choice => parse(choice.text)))
+			? concat((data.poll.choices as IChoice[]).map(choice => parse(choice.text.replace(/^<\/?!?nya>/ig, ''))))
 			: [];
 
 		const combinedTokens = tokens.concat(cwTokens).concat(choiceTokens);
@@ -303,7 +315,7 @@ export default async (user: IUser, data: Option, silent = false) => new Promise<
 
 	// If it is renote
 	if (data.renote) {
-		const type = data.text ? 'quote' : 'renote';
+		const type = data.text && data.text.replace(/^<\/?!?nya>/ig, '') ? 'quote' : 'renote';
 
 		// Notify
 		if (isLocalUser(data.renote._user)) {
@@ -339,7 +351,7 @@ export default async (user: IUser, data: Option, silent = false) => new Promise<
 async function renderActivity(data: Option, note: INote) {
 	if (data.localOnly) return null;
 
-	const content = data.renote && data.text == null && data.poll == null && (data.files == null || data.files.length == 0)
+	const content = data.renote && !data.text && !data.text.replace(/^<\/?!?nya>/ig, '') && !data.poll && (!data.files || !data.files.length)
 		? renderAnnounce(data.renote.uri ? data.renote.uri : `${config.url}/notes/${data.renote._id}`, note)
 		: renderCreate(await renderNote(note, false), note);
 
@@ -484,15 +496,17 @@ async function insertNote(user: IUser, data: Option, tags: string[], emojis: str
 }
 
 function index(note: INote) {
-	if (note.text == null || config.elasticsearch == null) return;
+	if (!note.text || !config.elasticsearch) return;
+
+	const text = note.text.replace(/^<\/?!?nya>/ig, '');
+
+	if (!text) return;
 
 	es.index({
 		index: 'misskey',
 		type: 'note',
 		id: note._id.toString(),
-		body: {
-			text: note.text
-		}
+		body: { text }
 	});
 }
 
diff --git a/test/api.ts b/test/api.ts
index 72a0efbbd..7f26b95bf 100644
--- a/test/api.ts
+++ b/test/api.ts
@@ -369,6 +369,52 @@ describe('API', () => {
 			expect(res).have.status(400);
 		}));
 
+		it('can make nyanize enable', async(async () => {
+			const me = await signup();
+
+			const post = {
+				text: 'なん<nya>なん<!nya>なん</!nya>なん</nya>なん'
+			};
+
+			const res = await request('/notes/create', post, me);
+
+			expect(res).have.status(200);
+			expect(res.body).be.a('object');
+			expect(res.body).have.property('createdNote');
+			expect(res.body.createdNote).have.property('text').eql('なんにゃんなんにゃんなん');
+		}));
+
+		it('can make nyanize disable', async(async () => {
+			const me = await signup();
+
+			await request('/i/update', {
+				isCat: true
+			}, me);
+
+			const post = {
+				text: 'なん<!nya>なん<nya>なん</nya>なん</!nya>なん'
+			};
+
+			const res = await request('/notes/create', post, me);
+
+			expect(res).have.status(200);
+			expect(res.body).be.a('object');
+			expect(res.body).have.property('createdNote');
+			expect(res.body.createdNote).have.property('text').eql('にゃんなんにゃんなんにゃん');
+		}));
+
+		it('throw error when invalid syntax', async(async () => {
+			const me = await signup();
+
+			const post = {
+				text: 'なん<nya>なん'
+			};
+
+			const res = await request('/notes/create', post, me);
+
+			expect(res).have.status(400);
+		}));
+
 		it('存在しないリプライ先で怒られる', async(async () => {
 			const me = await signup();
 			const post = {