diff --git a/CHANGELOG.md b/CHANGELOG.md
index f9ccaa9f1e80ed9321c8172be38057d671138902..c4da82e0a1a473afe85a609b276be619eac4fa8c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -41,6 +41,7 @@
 ### Server
 - Enhance: タイムライン取得時のパフォーマンスを大幅に向上
 - Enhance: ハイライト取得時のパフォーマンスを大幅に向上
+- Enhance: トレンドハッシュタグ取得時のパフォーマンスを大幅に向上
 - Enhance: 不要なPostgreSQLのインデックスを削除しパフォーマンスを向上
 
 ## 2023.9.3
diff --git a/packages/backend/src/core/FeaturedService.ts b/packages/backend/src/core/FeaturedService.ts
index 945c23b0e24ed371ca59151a28ce021f54be1c48..62b50ed38d0e3de80fe42708a58053742346e832 100644
--- a/packages/backend/src/core/FeaturedService.ts
+++ b/packages/backend/src/core/FeaturedService.ts
@@ -11,6 +11,7 @@ import { bindThis } from '@/decorators.js';
 
 const GLOBAL_NOTES_RANKING_WINDOW = 1000 * 60 * 60 * 24 * 3; // 3日ごと
 const PER_USER_NOTES_RANKING_WINDOW = 1000 * 60 * 60 * 24 * 7; // 1週間ごと
+const HASHTAG_RANKING_WINDOW = 1000 * 60 * 60; // 1時間ごと
 
 @Injectable()
 export class FeaturedService {
@@ -88,6 +89,11 @@ export class FeaturedService {
 		return this.updateRankingOf(`featuredPerUserNotesRanking:${userId}`, PER_USER_NOTES_RANKING_WINDOW, noteId, score);
 	}
 
+	@bindThis
+	public updateHashtagsRanking(hashtag: string, score = 1): Promise<void> {
+		return this.updateRankingOf('featuredHashtagsRanking', HASHTAG_RANKING_WINDOW, hashtag, score);
+	}
+
 	@bindThis
 	public getGlobalNotesRanking(limit: number): Promise<MiNote['id'][]> {
 		return this.getRankingOf('featuredGlobalNotesRanking', GLOBAL_NOTES_RANKING_WINDOW, limit);
@@ -102,4 +108,9 @@ export class FeaturedService {
 	public getPerUserNotesRanking(userId: MiUser['id'], limit: number): Promise<MiNote['id'][]> {
 		return this.getRankingOf(`featuredPerUserNotesRanking:${userId}`, PER_USER_NOTES_RANKING_WINDOW, limit);
 	}
+
+	@bindThis
+	public getHashtagsRanking(limit: number): Promise<string[]> {
+		return this.getRankingOf('featuredHashtagsRanking', HASHTAG_RANKING_WINDOW, limit);
+	}
 }
diff --git a/packages/backend/src/core/HashtagService.ts b/packages/backend/src/core/HashtagService.ts
index c72c7460ff21bb00264e77cb4c37de49e6b7516a..4900fa90a138f898a46d5af08edac8df7a5de1de 100644
--- a/packages/backend/src/core/HashtagService.ts
+++ b/packages/backend/src/core/HashtagService.ts
@@ -4,6 +4,8 @@
  */
 
 import { Inject, Injectable } from '@nestjs/common';
+import * as Redis from 'ioredis';
+import { getLineAndCharacterOfPosition } from 'typescript';
 import { DI } from '@/di-symbols.js';
 import type { MiUser } from '@/models/User.js';
 import { normalizeForSearch } from '@/misc/normalize-for-search.js';
@@ -12,14 +14,19 @@ import type { MiHashtag } from '@/models/Hashtag.js';
 import type { HashtagsRepository } from '@/models/_.js';
 import { UserEntityService } from '@/core/entities/UserEntityService.js';
 import { bindThis } from '@/decorators.js';
+import { FeaturedService } from '@/core/FeaturedService.js';
 
 @Injectable()
 export class HashtagService {
 	constructor(
+		@Inject(DI.redis)
+		private redisClient: Redis.Redis, // TODO: 専用のRedisサーバーを設定できるようにする
+
 		@Inject(DI.hashtagsRepository)
 		private hashtagsRepository: HashtagsRepository,
 
 		private userEntityService: UserEntityService,
+		private featuredService: FeaturedService,
 		private idService: IdService,
 	) {
 	}
@@ -46,6 +53,9 @@ export class HashtagService {
 	public async updateHashtag(user: { id: MiUser['id']; host: MiUser['host']; }, tag: string, isUserAttached = false, inc = true) {
 		tag = normalizeForSearch(tag);
 
+		// TODO: サンプリング
+		this.updateHashtagsRanking(tag, user.id);
+
 		const index = await this.hashtagsRepository.findOneBy({ name: tag });
 
 		if (index == null && !inc) return;
@@ -85,7 +95,7 @@ export class HashtagService {
 					}
 				}
 			} else {
-			// 自分が初めてこのタグを使ったなら
+				// 自分が初めてこのタグを使ったなら
 				if (!index.mentionedUserIds.some(id => id === user.id)) {
 					set.mentionedUserIds = () => `array_append("mentionedUserIds", '${user.id}')`;
 					set.mentionedUsersCount = () => '"mentionedUsersCount" + 1';
@@ -144,4 +154,93 @@ export class HashtagService {
 			}
 		}
 	}
+
+	@bindThis
+	public async updateHashtagsRanking(hashtag: string, userId: MiUser['id']): Promise<void> {
+		// TODO: instance.hiddenTagsの考慮
+
+		// YYYYMMDDHHmm (10分間隔)
+		const now = new Date();
+		now.setMinutes(Math.floor(now.getMinutes() / 10) * 10, 0, 0);
+		const window = `${now.getUTCFullYear()}${(now.getUTCMonth() + 1).toString().padStart(2, '0')}${now.getUTCDate().toString().padStart(2, '0')}${now.getUTCHours().toString().padStart(2, '0')}${now.getUTCMinutes().toString().padStart(2, '0')}`;
+
+		const exist = await this.redisClient.sismember(`hashtagUsers:${hashtag}`, userId);
+		if (exist === 1) return;
+
+		this.featuredService.updateHashtagsRanking(hashtag, 1);
+
+		const redisPipeline = this.redisClient.pipeline();
+
+		// TODO: これらの Set は Bloom Filter を使うようにしても良さそう
+
+		// チャート用
+		redisPipeline.sadd(`hashtagUsers:${hashtag}:${window}`, userId);
+		redisPipeline.expire(`hashtagUsers:${hashtag}:${window}`,
+			60 * 60 * 24 * 3, // 3日間
+			'NX', // "NX -- Set expiry only when the key has no expiry" = 有効期限がないときだけ設定
+		);
+
+		// ユニークカウント用
+		redisPipeline.sadd(`hashtagUsers:${hashtag}`, userId);
+		redisPipeline.expire(`hashtagUsers:${hashtag}`,
+			60 * 60, // 1時間
+			'NX', // "NX -- Set expiry only when the key has no expiry" = 有効期限がないときだけ設定
+		);
+
+		redisPipeline.exec();
+	}
+
+	@bindThis
+	public async getChart(hashtag: string, range: number): Promise<number[]> {
+		const now = new Date();
+		now.setMinutes(Math.floor(now.getMinutes() / 10) * 10, 0, 0);
+
+		const redisPipeline = this.redisClient.pipeline();
+
+		for (let i = 0; i < range; i++) {
+			const window = `${now.getUTCFullYear()}${(now.getUTCMonth() + 1).toString().padStart(2, '0')}${now.getUTCDate().toString().padStart(2, '0')}${now.getUTCHours().toString().padStart(2, '0')}${now.getUTCMinutes().toString().padStart(2, '0')}`;
+			redisPipeline.scard(`hashtagUsers:${hashtag}:${window}`);
+			now.setMinutes(now.getMinutes() - (i * 10), 0, 0);
+		}
+
+		const result = await redisPipeline.exec();
+
+		if (result == null) return [];
+
+		return result.map(x => x[1]) as number[];
+	}
+
+	@bindThis
+	public async getCharts(hashtags: string[], range: number): Promise<Record<string, number[]>> {
+		const now = new Date();
+		now.setMinutes(Math.floor(now.getMinutes() / 10) * 10, 0, 0);
+
+		const redisPipeline = this.redisClient.pipeline();
+
+		for (let i = 0; i < range; i++) {
+			const window = `${now.getUTCFullYear()}${(now.getUTCMonth() + 1).toString().padStart(2, '0')}${now.getUTCDate().toString().padStart(2, '0')}${now.getUTCHours().toString().padStart(2, '0')}${now.getUTCMinutes().toString().padStart(2, '0')}`;
+			for (const hashtag of hashtags) {
+				redisPipeline.scard(`hashtagUsers:${hashtag}:${window}`);
+			}
+			now.setMinutes(now.getMinutes() - (i * 10), 0, 0);
+		}
+
+		const result = await redisPipeline.exec();
+
+		if (result == null) return {};
+
+		// key is hashtag
+		const charts = {} as Record<string, number[]>;
+		for (const hashtag of hashtags) {
+			charts[hashtag] = [];
+		}
+
+		for (let i = 0; i < range; i++) {
+			for (let j = 0; j < hashtags.length; j++) {
+				charts[hashtags[j]].push(result[(i * hashtags.length) + j][1] as number);
+			}
+		}
+
+		return charts;
+	}
 }
diff --git a/packages/backend/src/server/api/endpoints/hashtags/trend.ts b/packages/backend/src/server/api/endpoints/hashtags/trend.ts
index 75d4fe3819b387de8b5c4719eef74c907c6ab2c3..a69e007a400569482f17b923ee0517d0fbc440d5 100644
--- a/packages/backend/src/server/api/endpoints/hashtags/trend.ts
+++ b/packages/backend/src/server/api/endpoints/hashtags/trend.ts
@@ -3,29 +3,13 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { Brackets } from 'typeorm';
 import { Inject, Injectable } from '@nestjs/common';
 import { Endpoint } from '@/server/api/endpoint-base.js';
-import type { NotesRepository } from '@/models/_.js';
-import type { MiNote } from '@/models/Note.js';
-import { safeForSql } from '@/misc/safe-for-sql.js';
 import { normalizeForSearch } from '@/misc/normalize-for-search.js';
 import { MetaService } from '@/core/MetaService.js';
 import { DI } from '@/di-symbols.js';
-
-/*
-トレンドに載るためには「『直近a分間のユニーク投稿数が今からa分前～今からb分前の間のユニーク投稿数のn倍以上』のハッシュタグの上位5位以内に入る」ことが必要
-ユニーク投稿数とはそのハッシュタグと投稿ユーザーのペアのカウントで、例えば同じユーザーが複数回同じハッシュタグを投稿してもそのハッシュタグのユニーク投稿数は1とカウントされる
-
-..が理想だけどPostgreSQLでどうするのか分からないので単に「直近Aの内に投稿されたユニーク投稿数が多いハッシュタグ」で妥協する
-*/
-
-const rangeA = 1000 * 60 * 60; // 60分
-//const rangeB = 1000 * 60 * 120; // 2時間
-//const coefficient = 1.25; // 「n倍」の部分
-//const requiredUsers = 3; // 最低何人がそのタグを投稿している必要があるか
-
-const max = 5;
+import { FeaturedService } from '@/core/FeaturedService.js';
+import { HashtagService } from '@/core/HashtagService.js';
 
 export const meta = {
 	tags: ['hashtags'],
@@ -71,98 +55,22 @@ export const paramDef = {
 @Injectable()
 export default class extends Endpoint<typeof meta, typeof paramDef> { // eslint-disable-line import/no-default-export
 	constructor(
-		@Inject(DI.notesRepository)
-		private notesRepository: NotesRepository,
-
 		private metaService: MetaService,
+		private featuredService: FeaturedService,
+		private hashtagService: HashtagService,
 	) {
 		super(meta, paramDef, async () => {
 			const instance = await this.metaService.fetch(true);
 			const hiddenTags = instance.hiddenTags.map(t => normalizeForSearch(t));
 
-			const now = new Date(); // 5分単位で丸めた現在日時
-			now.setMinutes(Math.round(now.getMinutes() / 5) * 5, 0, 0);
-
-			const tagNotes = await this.notesRepository.createQueryBuilder('note')
-				.where('note.createdAt > :date', { date: new Date(now.getTime() - rangeA) })
-				.andWhere(new Brackets(qb => { qb
-					.where('note.visibility = \'public\'')
-					.orWhere('note.visibility = \'home\'');
-				}))
-				.andWhere('note.tags != \'{}\'')
-				.select(['note.tags', 'note.userId'])
-				.cache(60000) // 1 min
-				.getMany();
-
-			if (tagNotes.length === 0) {
-				return [];
-			}
-
-			const tags: {
-		name: string;
-		users: MiNote['userId'][];
-	}[] = [];
-
-			for (const note of tagNotes) {
-				for (const tag of note.tags) {
-					if (hiddenTags.includes(tag)) continue;
-
-					const x = tags.find(x => x.name === tag);
-					if (x) {
-						if (!x.users.includes(note.userId)) {
-							x.users.push(note.userId);
-						}
-					} else {
-						tags.push({
-							name: tag,
-							users: [note.userId],
-						});
-					}
-				}
-			}
-
-			// タグを人気順に並べ替え
-			const hots = tags
-				.sort((a, b) => b.users.length - a.users.length)
-				.map(tag => tag.name)
-				.slice(0, max);
-
-			//#region 2(または3)で話題と判定されたタグそれぞれについて過去の投稿数グラフを取得する
-			const countPromises: Promise<number[]>[] = [];
-
-			const range = 20;
-
-			// 10分
-			const interval = 1000 * 60 * 10;
-
-			for (let i = 0; i < range; i++) {
-				countPromises.push(Promise.all(hots.map(tag => this.notesRepository.createQueryBuilder('note')
-					.select('count(distinct note.userId)')
-					.where(`'{"${safeForSql(tag) ? tag : 'aichan_kawaii'}"}' <@ note.tags`)
-					.andWhere('note.createdAt < :lt', { lt: new Date(now.getTime() - (interval * i)) })
-					.andWhere('note.createdAt > :gt', { gt: new Date(now.getTime() - (interval * (i + 1))) })
-					.cache(60000) // 1 min
-					.getRawOne()
-					.then(x => parseInt(x.count, 10)),
-				)));
-			}
-
-			const countsLog = await Promise.all(countPromises);
-			//#endregion
+			const ranking = await this.featuredService.getHashtagsRanking(10);
 
-			const totalCounts = await Promise.all(hots.map(tag => this.notesRepository.createQueryBuilder('note')
-				.select('count(distinct note.userId)')
-				.where(`'{"${safeForSql(tag) ? tag : 'aichan_kawaii'}"}' <@ note.tags`)
-				.andWhere('note.createdAt > :gt', { gt: new Date(now.getTime() - rangeA) })
-				.cache(60000 * 60) // 60 min
-				.getRawOne()
-				.then(x => parseInt(x.count, 10)),
-			));
+			const charts = ranking.length === 0 ? {} : await this.hashtagService.getCharts(ranking, 20);
 
-			const stats = hots.map((tag, i) => ({
+			const stats = ranking.map((tag, i) => ({
 				tag,
-				chart: countsLog.map(counts => counts[i]),
-				usersCount: totalCounts[i],
+				chart: charts[tag],
+				usersCount: Math.max(...charts[tag]),
 			}));
 
 			return stats;