diff --git a/ext/js/language/ja/japanese-text-preprocessors.js b/ext/js/language/ja/japanese-text-preprocessors.js
index 2ec883d290..e6e6ad3b70 100644
--- a/ext/js/language/ja/japanese-text-preprocessors.js
+++ b/ext/js/language/ja/japanese-text-preprocessors.js
@@ -95,3 +95,29 @@ export const standardizeKanji = {
     description: '萬 → 万',
     process: (str) => [str, convertVariants(str)],
 };
+
+const WILDCARD_MAX_VARIANTS = 51;
+const WILDCARD_CHAR = '～'; // U+FF5E fullwidth tilde
+
+/** @type {import('language').TextProcessor} */
+export const insertWildcard = {
+    name: 'Insert wildcard for grammar patterns',
+    description: 'いくら騒いでも → いくら～でも',
+    process: (str) => {
+        const chars = [...str];
+        const n = chars.length;
+        if (n < 3) { return [str]; }
+
+        /** @type {string[]} */
+        const results = [str];
+        for (let prefixLen = 1; prefixLen < n; prefixLen++) {
+            for (let suffixLen = 1; suffixLen < n - prefixLen; suffixLen++) {
+                const prefix = chars.slice(0, prefixLen).join('');
+                const suffix = chars.slice(n - suffixLen).join('');
+                results.push(prefix + WILDCARD_CHAR + suffix);
+                if (results.length >= WILDCARD_MAX_VARIANTS) { return results; }
+            }
+        }
+        return results;
+    },
+};
diff --git a/ext/js/language/language-descriptors.js b/ext/js/language/language-descriptors.js
index 613d4fc723..543dfccaae 100644
--- a/ext/js/language/language-descriptors.js
+++ b/ext/js/language/language-descriptors.js
@@ -46,6 +46,7 @@ import {
     collapseEmphaticSequences,
     convertHalfWidthCharacters,
     convertHiraganaToKatakana,
+    insertWildcard,
     normalizeCJKCompatibilityCharacters,
     normalizeCombiningCharacters,
     standardizeKanji,
@@ -355,6 +356,7 @@ const languageDescriptors = [
             convertHiraganaToKatakana,
             collapseEmphaticSequences,
             standardizeKanji,
+            insertWildcard,
         },
         languageTransforms: japaneseTransforms,
     },
diff --git a/test/language/japanese-text-preprocessors.test.js b/test/language/japanese-text-preprocessors.test.js
new file mode 100644
index 0000000000..ff8c62e0e8
--- /dev/null
+++ b/test/language/japanese-text-preprocessors.test.js
@@ -0,0 +1,91 @@
+/*
+ * Copyright (C) 2024-2026  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/>.
+ */
+
+import {describe, expect, test} from 'vitest';
+import {insertWildcard} from '../../ext/js/language/ja/japanese-text-preprocessors.js';
+
+const {process} = insertWildcard;
+
+describe('insertWildcard', () => {
+    test('short input (1 char) returns only original', () => {
+        expect(process('あ')).toStrictEqual(['あ']);
+    });
+
+    test('short input (2 chars) returns only original', () => {
+        expect(process('あい')).toStrictEqual(['あい']);
+    });
+
+    test('3-char input produces 1 wildcard variant', () => {
+        const variants = process('あいう');
+        expect(variants).toContain('あいう');
+        expect(variants).toContain('あ～う');
+        expect(variants).toHaveLength(2);
+    });
+
+    test('いくら騒いでも produces いくら～でも', () => {
+        const variants = process('いくら騒いでも');
+        expect(variants).toContain('いくら騒いでも');
+        expect(variants).toContain('いくら～でも');
+    });
+
+    test('single-char prefix works for ば～ほど pattern', () => {
+        const variants = process('ば食べるほど');
+        expect(variants).toContain('ば食べるほど');
+        expect(variants).toContain('ば～ほど');
+    });
+
+    test('しか～ない pattern works', () => {
+        const variants = process('しか言わない');
+        expect(variants).toContain('しか言わない');
+        expect(variants).toContain('しか～ない');
+    });
+
+    test('wildcard character is fullwidth tilde U+FF5E', () => {
+        const variants = process('あいう');
+        const wildcardVariant = variants.find((v) => v !== 'あいう');
+        expect(wildcardVariant).toBe('あ\uFF5Eう');
+    });
+
+    test('variant count for 5-char input', () => {
+        // n=5: prefixLen 1..3, for each suffixLen 1..(n-prefixLen-1)
+        // p=1: s=1,2,3 (3); p=2: s=1,2 (2); p=3: s=1 (1) = 6 variants + original
+        const variants = process('あいうえお');
+        expect(variants).toHaveLength(7);
+    });
+
+    test('variant count for 7-char input', () => {
+        // (n-1)(n-2)/2 = 6*5/2 = 15 variants + original
+        const variants = process('あいうえおかき');
+        expect(variants).toHaveLength(16);
+    });
+
+    test('variants are capped at 51 for long inputs', () => {
+        const longStr = 'あいうえおかきくけこさしすせそ'; // 15 chars
+        const variants = process(longStr);
+        expect(variants).toHaveLength(51);
+    });
+
+    test('empty string returns only original', () => {
+        expect(process('')).toStrictEqual(['']);
+    });
+
+    test('original string is always first', () => {
+        const input = 'いくら騒いでも';
+        const variants = process(input);
+        expect(variants[0]).toBe(input);
+    });
+});
diff --git a/types/ext/language-descriptors.d.ts b/types/ext/language-descriptors.d.ts
index cfee329e79..0060386d14 100644
--- a/types/ext/language-descriptors.d.ts
+++ b/types/ext/language-descriptors.d.ts
@@ -194,6 +194,7 @@ type AllTextProcessors = {
             convertHiraganaToKatakana: TextProcessor;
             collapseEmphaticSequences: TextProcessor;
             standardizeKanji: TextProcessor;
+            insertWildcard: TextProcessor;
         };
     };
     ka: Record<string, never>;