diff --git a/.eslintrc.json b/.eslintrc.json
index 62ee61da60..d19428666e 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -638,6 +638,7 @@
                 "ext/js/language/en/english-transforms.js",
                 "ext/js/language/es/spanish-transforms.js",
                 "ext/js/language/ja/japanese-text-preprocessors.js",
+                "ext/js/language/ja/shinjitai-converter.js",
                 "ext/js/language/ja/japanese-transforms.js",
                 "ext/js/language/ja/japanese-wanakana.js",
                 "ext/js/language/ja/japanese.js",
diff --git a/ext/js/language/ja/japanese-text-preprocessors.js b/ext/js/language/ja/japanese-text-preprocessors.js
index cdd8ce9ad9..62bf626c2d 100644
--- a/ext/js/language/ja/japanese-text-preprocessors.js
+++ b/ext/js/language/ja/japanese-text-preprocessors.js
@@ -26,6 +26,7 @@ import {
     convertKatakanaToHiragana as convertKatakanaToHiraganaFunction,
     normalizeCombiningCharacters as normalizeCombiningCharactersFunction,
 } from './japanese.js';
+import {convertShinjitai as convertShinjitaiFunction} from './shinjitai-converter.js';
 
 /** @type {import('language').TextProcessor<boolean>} */
 export const convertHalfWidthCharacters = {
@@ -99,3 +100,11 @@ export const normalizeCombiningCharacters = {
     options: basicTextProcessorOptions,
     process: (str, setting) => (setting ? normalizeCombiningCharactersFunction(str) : str),
 };
+
+/** @type {import('language').TextProcessor<boolean>} */
+export const convertShinjitai = {
+    name: 'Convert Kyujitai to Shinjitai',
+    description: '萬 → 万',
+    options: basicTextProcessorOptions,
+    process: (str, setting) => (setting ? convertShinjitaiFunction(str) : str),
+};
diff --git a/ext/js/language/ja/shinjitai-converter.js b/ext/js/language/ja/shinjitai-converter.js
new file mode 100644
index 0000000000..430d999089
--- /dev/null
+++ b/ext/js/language/ja/shinjitai-converter.js
@@ -0,0 +1,584 @@
+/*
+ * Copyright (C) 2024  Yomitan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/**
+ * Map used to convert 旧字体 (Kyujitai) to 新字体 (Shinjitai), compiled from various sources.
+ * This map does not include transformations caused by the 同音による書き換え reform.
+ * This map does not include 俗字, 別体, 誤字 or other uncommon forms or variants.
+ */
+const shinjitaiMap = new Map([
+    //  A source comment signifies that the entries below are from that source and not included in any of the above ones.
+
+    /* https://github.com/DrTurnon/kyujipy */
+
+    // 常用漢字
+    ['亞', '亜'],
+    ['惡', '悪'],
+    ['壓', '圧'],
+    ['圍', '囲'],
+    ['醫', '医'],
+    ['爲', '為'],
+    ['壹', '壱'],
+    ['逸', '逸'],
+    ['飮', '飲'],
+    ['隱', '隠'],
+    ['羽', '羽'],
+    ['榮', '栄'],
+    ['營', '営'],
+    ['銳', '鋭'],
+    ['衞', '衛'],
+    ['益', '益'],
+    ['驛', '駅'],
+    ['悅', '悦'],
+    ['謁', '謁'],
+    ['閱', '閲'],
+    ['圓', '円'],
+    ['鹽', '塩'],
+    ['緣', '縁'],
+    ['艷', '艶'],
+    ['應', '応'],
+    ['歐', '欧'],
+    ['毆', '殴'],
+    ['櫻', '桜'],
+    ['奧', '奥'],
+    ['橫', '横'],
+    ['溫', '温'],
+    ['穩', '穏'],
+    ['假', '仮'],
+    ['價', '価'],
+    ['禍', '禍'],
+    ['畫', '画'],
+    ['會', '会'],
+    ['悔', '悔'],
+    ['海', '海'],
+    ['繪', '絵'],
+    ['壞', '壊'],
+    ['懷', '懐'],
+    ['慨', '慨'],
+    ['槪', '概'],
+    ['擴', '拡'],
+    ['殼', '殻'],
+    ['覺', '覚'],
+    ['學', '学'],
+    ['嶽', '岳'],
+    ['樂', '楽'],
+    ['喝', '喝'],
+    ['渴', '渇'],
+    ['褐', '褐'],
+    ['罐', '缶'],
+    ['卷', '巻'],
+    ['陷', '陥'],
+    ['勸', '勧'],
+    ['寬', '寛'],
+    ['漢', '漢'],
+    ['關', '関'],
+    ['歡', '歓'],
+    ['館', '館'],
+    ['觀', '観'],
+    ['顏', '顔'],
+    ['氣', '気'],
+    ['祈', '祈'],
+    ['既', '既'],
+    ['歸', '帰'],
+    ['龜', '亀'],
+    ['器', '器'],
+    ['僞', '偽'],
+    ['戲', '戯'],
+    ['犧', '犠'],
+    ['舊', '旧'],
+    ['據', '拠'],
+    ['擧', '挙'],
+    ['虛', '虚'],
+    ['峽', '峡'],
+    ['挾', '挟'],
+    ['狹', '狭'],
+    ['敎', '教'],
+    ['鄕', '郷'],
+    ['響', '響'],
+    ['曉', '暁'],
+    ['勤', '勤'],
+    ['謹', '謹'],
+    ['區', '区'],
+    ['驅', '駆'],
+    ['勳', '勲'],
+    ['薰', '薫'],
+    ['徑', '径'],
+    ['莖', '茎'],
+    ['契', '契'],
+    ['惠', '恵'],
+    ['揭', '掲'],
+    ['溪', '渓'],
+    ['經', '経'],
+    ['螢', '蛍'],
+    ['輕', '軽'],
+    ['繼', '継'],
+    ['鷄', '鶏'],
+    ['藝', '芸'],
+    ['擊', '撃'],
+    ['缺', '欠'],
+    ['硏', '研'],
+    ['縣', '県'],
+    ['儉', '倹'],
+    ['劍', '剣'],
+    ['險', '険'],
+    ['圈', '圏'],
+    ['檢', '検'],
+    ['獻', '献'],
+    ['權', '権'],
+    ['顯', '顕'],
+    ['驗', '験'],
+    ['嚴', '厳'],
+    ['戶', '戸'],
+    ['吳', '呉'],
+    ['娛', '娯'],
+    ['廣', '広'],
+    ['效', '効'],
+    ['恆', '恒'],
+    ['黃', '黄'],
+    ['鑛', '鉱'],
+    ['號', '号'],
+    ['吿', '告'],
+    ['國', '国'],
+    ['黑', '黒'],
+    ['穀', '穀'],
+    ['碎', '砕'],
+    ['濟', '済'],
+    ['齋', '斎'],
+    ['歲', '歳'],
+    ['劑', '剤'],
+    ['殺', '殺'],
+    ['雜', '雑'],
+    ['參', '参'],
+    ['棧', '桟'],
+    ['蠶', '蚕'],
+    ['慘', '惨'],
+    ['產', '産'],
+    ['贊', '賛'],
+    ['殘', '残'],
+    ['絲', '糸'],
+    ['祉', '祉'],
+    ['視', '視'],
+    ['齒', '歯'],
+    ['飼', '飼'],
+    ['兒', '児'],
+    ['辭', '辞'],
+    ['濕', '湿'],
+    ['實', '実'],
+    ['寫', '写'],
+    ['社', '社'],
+    ['舍', '舎'],
+    ['者', '者'],
+    ['煮', '煮'],
+    ['釋', '釈'],
+    ['壽', '寿'],
+    ['收', '収'],
+    ['臭', '臭'],
+    ['從', '従'],
+    ['澁', '渋'],
+    ['獸', '獣'],
+    ['縱', '縦'],
+    ['祝', '祝'],
+    ['肅', '粛'],
+    ['處', '処'],
+    ['暑', '暑'],
+    ['署', '署'],
+    ['緖', '緒'],
+    ['諸', '諸'],
+    ['敍', '叙'],
+    ['尙', '尚'],
+    ['將', '将'],
+    ['祥', '祥'],
+    ['稱', '称'],
+    ['涉', '渉'],
+    ['燒', '焼'],
+    ['證', '証'],
+    ['奬', '奨'],
+    ['條', '条'],
+    ['狀', '状'],
+    ['乘', '乗'],
+    ['淨', '浄'],
+    ['剩', '剰'],
+    ['疊', '畳'],
+    ['繩', '縄'],
+    ['壤', '壌'],
+    ['孃', '嬢'],
+    ['讓', '譲'],
+    ['釀', '醸'],
+    ['觸', '触'],
+    ['囑', '嘱'],
+    ['神', '神'],
+    ['眞', '真'],
+    ['寢', '寝'],
+    ['愼', '慎'],
+    ['盡', '尽'],
+    ['圖', '図'],
+    ['粹', '粋'],
+    ['醉', '酔'],
+    ['穗', '穂'],
+    ['隨', '随'],
+    ['髓', '髄'],
+    ['樞', '枢'],
+    ['數', '数'],
+    ['瀨', '瀬'],
+    ['聲', '声'],
+    ['靑', '青'],
+    ['齊', '斉'],
+    ['淸', '清'],
+    ['晴', '晴'],
+    ['精', '精'],
+    ['靜', '静'],
+    ['稅', '税'],
+    ['竊', '窃'],
+    ['攝', '摂'],
+    ['節', '節'],
+    ['說', '説'],
+    ['絕', '絶'],
+    ['專', '専'],
+    ['淺', '浅'],
+    ['戰', '戦'],
+    ['踐', '践'],
+    ['錢', '銭'],
+    ['潛', '潜'],
+    ['纖', '繊'],
+    ['禪', '禅'],
+    ['祖', '祖'],
+    ['雙', '双'],
+    ['壯', '壮'],
+    ['爭', '争'],
+    ['莊', '荘'],
+    ['搜', '捜'],
+    ['插', '挿'],
+    ['巢', '巣'],
+    ['曾', '曽'],
+    ['瘦', '痩'],
+    ['裝', '装'],
+    ['僧', '僧'],
+    ['層', '層'],
+    ['總', '総'],
+    ['騷', '騒'],
+    ['增', '増'],
+    ['憎', '憎'],
+    ['藏', '蔵'],
+    ['贈', '贈'],
+    ['臟', '臓'],
+    ['卽', '即'],
+    ['屬', '属'],
+    ['續', '続'],
+    ['墮', '堕'],
+    ['對', '対'],
+    ['體', '体'],
+    ['帶', '帯'],
+    ['滯', '滞'],
+    ['臺', '台'],
+    ['瀧', '滝'],
+    ['擇', '択'],
+    ['澤', '沢'],
+    ['脫', '脱'],
+    ['擔', '担'],
+    ['單', '単'],
+    ['膽', '胆'],
+    ['嘆', '嘆'],
+    ['團', '団'],
+    ['斷', '断'],
+    ['彈', '弾'],
+    ['遲', '遅'],
+    ['癡', '痴'],
+    ['蟲', '虫'],
+    ['晝', '昼'],
+    ['鑄', '鋳'],
+    ['著', '著'],
+    ['廳', '庁'],
+    ['徵', '徴'],
+    ['聽', '聴'],
+    ['懲', '懲'],
+    ['敕', '勅'],
+    ['鎭', '鎮'],
+    ['塚', '塚'],
+    ['遞', '逓'],
+    ['鐵', '鉄'],
+    ['點', '点'],
+    ['轉', '転'],
+    ['傳', '伝'],
+    ['都', '都'],
+    ['燈', '灯'],
+    ['當', '当'],
+    ['黨', '党'],
+    ['盜', '盗'],
+    ['稻', '稲'],
+    ['鬭', '闘'],
+    ['德', '徳'],
+    ['獨', '独'],
+    ['讀', '読'],
+    ['突', '突'],
+    ['屆', '届'],
+    ['內', '内'],
+    ['難', '難'],
+    ['貳', '弐'],
+    ['腦', '悩'],
+    ['腦', '脳'],
+    ['霸', '覇'],
+    ['拜', '拝'],
+    ['廢', '廃'],
+    ['賣', '売'],
+    ['梅', '梅'],
+    ['麥', '麦'],
+    ['發', '発'],
+    ['髮', '髪'],
+    ['拔', '抜'],
+    ['飯', '飯'],
+    ['繁', '繁'],
+    ['晚', '晩'],
+    ['蠻', '蛮'],
+    ['卑', '卑'],
+    ['祕', '秘'],
+    ['碑', '碑'],
+    ['濱', '浜'],
+    ['賓', '賓'],
+    ['頻', '頻'],
+    ['敏', '敏'],
+    ['甁', '瓶'],
+    ['侮', '侮'],
+    ['福', '福'],
+    ['拂', '払'],
+    ['佛', '仏'],
+    ['倂', '併'],
+    ['竝', '並'],
+    ['塀', '塀'],
+    ['餠', '餅'],
+    ['邊', '辺'],
+    ['變', '変'],
+    ['勉', '勉'],
+    ['步', '歩'],
+    ['舖', '舗'],
+    ['寶', '宝'],
+    ['豐', '豊'],
+    ['襃', '褒'],
+    ['墨', '墨'],
+    ['沒', '没'],
+    ['飜', '翻'],
+    ['每', '毎'],
+    ['萬', '万'],
+    ['滿', '満'],
+    ['免', '免'],
+    ['麵', '麺'],
+    ['默', '黙'],
+    ['彌', '弥'],
+    ['譯', '訳'],
+    ['藥', '薬'],
+    ['與', '与'],
+    ['豫', '予'],
+    ['餘', '余'],
+    ['譽', '誉'],
+    ['搖', '揺'],
+    ['樣', '様'],
+    ['謠', '謡'],
+    ['來', '来'],
+    ['賴', '頼'],
+    ['亂', '乱'],
+    ['覽', '覧'],
+    ['欄', '欄'],
+    ['龍', '竜'],
+    ['隆', '隆'],
+    ['旅', '旅'],
+    ['虜', '虜'],
+    ['兩', '両'],
+    ['獵', '猟'],
+    ['綠', '緑'],
+    ['淚', '涙'],
+    ['壘', '塁'],
+    ['類', '類'],
+    ['禮', '礼'],
+    ['勵', '励'],
+    ['戾', '戻'],
+    ['靈', '霊'],
+    ['隸', '隷'],
+    ['齡', '齢'],
+    ['曆', '暦'],
+    ['歷', '歴'],
+    ['戀', '恋'],
+    ['連', '連'],
+    ['廉', '廉'],
+    ['練', '練'],
+    ['鍊', '錬'],
+    ['爐', '炉'],
+    ['勞', '労'],
+    ['郞', '郎'],
+    ['朗', '朗'],
+    ['廊', '廊'],
+    ['樓', '楼'],
+    ['籠', '篭'],
+    ['錄', '録'],
+    ['灣', '湾'],
+
+    // 人名用漢字
+    ['堯', '尭'],
+    ['巖', '巌'],
+    ['摑', '掴'],
+    ['彥', '彦'],
+    ['檜', '桧'],
+    ['槇', '槙'],
+    ['渚', '渚'],
+    ['猪', '猪'],
+    ['琢', '琢'],
+    ['瑤', '瑶'],
+    ['禰', '祢'],
+    ['祐', '祐'],
+    ['禱', '祷'],
+    ['祿', '禄'],
+    ['禎', '禎'],
+    ['穰', '穣'],
+    ['簞', '箪'],
+    ['聰', '聡'],
+    ['蓮', '蓮'],
+    ['蘭', '蘭'],
+    ['遙', '遥'],
+    ['遼', '遼'],
+    ['靖', '靖'],
+
+    // 表外字 (擴張新字體)
+    ['蘒', '蘒'],
+    ['啞', '唖'],
+    ['噓', '嘘'],
+    ['穎', '頴'],
+    ['鷗', '鴎'],
+    ['軀', '躯'],
+    ['鶯', '鴬'],
+    ['攪', '撹'],
+    ['麴', '麹'],
+    ['鹼', '鹸'],
+    ['嚙', '噛'],
+    ['繡', '繍'],
+    ['蔣', '蒋'],
+    ['醬', '醤'],
+    ['搔', '掻'],
+    ['屛', '屏'],
+    ['幷', '并'],
+    ['濾', '沪'],
+    ['蘆', '芦'],
+    ['蠟', '蝋'],
+    ['彎', '弯'],
+    ['焰', '焔'],
+    ['礦', '砿'],
+    ['讚', '讃'],
+    ['顚', '顛'],
+    ['巓', '巔'],
+    ['醱', '醗'],
+    ['潑', '溌'],
+    ['輛', '輌'],
+    ['繫', '繋'],
+    ['瀆', '涜'],
+    ['儘', '侭'],
+    ['藪', '薮'],
+    ['蠅', '蝿'],
+    ['嬀', '媯'],
+    ['驒', '騨'],
+
+    // variants
+
+    // 常用漢字
+    ['鬥', '闘'],
+    ['鬪', '闘'],
+    ['鬬', '闘'],
+
+    // 人名用漢字
+    ['亙', '亘'],
+    ['凜', '凛'],
+    ['晄', '晃'],
+    ['晉', '晋'],
+    ['萠', '萌'],
+
+    /* 新字源 */
+
+    ['冬', '冬'],
+    ['割', '割'],
+    ['勇', '勇'],
+    ['周', '周'],
+    ['噴', '噴'],
+    ['城', '城'],
+    ['墳', '墳'],
+    ['奔', '奔'],
+    ['姬', '姫'],
+    ['寧', '寧'],
+    ['瓣', '弁'],
+    ['辨', '弁'],
+    ['辯', '弁'],
+    ['彫', '彫'],
+    ['惱', '悩'],
+    ['慈', '慈'],
+    ['憤', '憤'],
+    ['憲', '憲'],
+    ['成', '成'],
+    ['戴', '戴'],
+    ['搜', '捜'],
+    ['滋', '滋'],
+    ['潮', '潮'],
+    ['炭', '炭'],
+    ['爵', '爵'],
+    ['異', '異'],
+    ['盛', '盛'],
+    ['𥔵', '磁'],
+    ['𥳑', '簡'],
+    ['糖', '糖'],
+    ['𦤶', '致'],
+    ['芽', '芽'],
+    ['若', '若'],
+    ['茶', '茶'],
+    ['華', '華'],
+    ['落', '落'],
+    ['葉', '葉'],
+    ['藍', '藍'],
+    ['覆', '覆'],
+    ['諭', '諭'],
+    ['諾', '諾'],
+    ['輸', '輸'],
+    ['閒', '間'],
+    ['降', '降'],
+
+    /* 三省堂 */
+    ['充', '充'],
+    ['册', '冊'],
+    ['勺', '勺'],
+    ['巽', '巽'],
+    ['强', '強'],
+    ['旣', '既'],
+    ['流', '流'],
+    ['浩', '浩'],
+    ['煕', '熙'],
+
+    /* 大修館 */
+    ['兔', '兎'],
+    ['廚', '厨'],
+    ['廏', '厩'],
+    ['壻', '婿'],
+    ['槪', '概'],
+]);
+
+let regexString = '';
+for (const [kyuji] of shinjitaiMap) {
+    regexString += kyuji;
+}
+const regex = new RegExp('[' + regexString + ']', 'g');
+
+/**
+ * @param {string} str
+ * @returns {string}
+ */
+export function convertShinjitai(str) {
+    return str.replace(regex, (c) => {
+        return shinjitaiMap.get(c) ?? c;
+    });
+}
diff --git a/ext/js/language/language-descriptors.js b/ext/js/language/language-descriptors.js
index 8277cee8bf..2b8b3f9b17 100644
--- a/ext/js/language/language-descriptors.js
+++ b/ext/js/language/language-descriptors.js
@@ -27,6 +27,7 @@ import {
     convertHalfWidthCharacters,
     convertHiraganaToKatakana,
     normalizeCombiningCharacters,
+    convertShinjitai,
 } from './ja/japanese-text-preprocessors.js';
 import {japaneseTransforms} from './ja/japanese-transforms.js';
 import {isStringPartiallyJapanese} from './ja/japanese.js';
@@ -200,6 +201,7 @@ const languageDescriptors = [
             alphanumericWidthVariants,
             convertHiraganaToKatakana,
             collapseEmphaticSequences,
+            convertShinjitai,
         },
         languageTransforms: japaneseTransforms,
     },
diff --git a/types/ext/language-descriptors.d.ts b/types/ext/language-descriptors.d.ts
index bcb1dfac2b..d9c95cd710 100644
--- a/types/ext/language-descriptors.d.ts
+++ b/types/ext/language-descriptors.d.ts
@@ -134,6 +134,7 @@ type AllTextProcessors = {
             alphanumericWidthVariants: BidirectionalConversionPreprocessor;
             convertHiraganaToKatakana: BidirectionalConversionPreprocessor;
             collapseEmphaticSequences: TextProcessor<[collapseEmphatic: boolean, collapseEmphaticFull: boolean]>;
+            convertShinjitai: TextProcessor<boolean>;
         };
     };
     ko: {