Fix Japanese IME Switching to Half-Width After Each Reboot on Windows 11

Quick fix: Open Settings → Time & language → Language & region → 日本語 → Language options → Microsoft IME → Keyboard options → General, and set Default input method to Hiragana. The IME will now boot in hiragana mode instead of half-width English after every reboot.

You set the Japanese IME to hiragana while typing. Worked fine all day. After a reboot, the IME starts in half-width English (A indicator) instead of hiragana (あ). You have to press Alt+~ or 半角/全角 every single time after sign-in to start typing Japanese. The IME forgot your last mode because the per-session default isn’t hiragana — it’s half-width.

What the “default input method” setting controls

The Japanese IME has a session-startup mode that determines which composition mode is active when the IME first loads. Microsoft’s default for new installs is half-width English — a reasonable choice for English-first users who occasionally type Japanese. For users whose primary language is Japanese, half-width English is wrong; they want hiragana by default.

The setting exists in IME options but is buried three levels deep in Settings. Most users never find it and just accept the daily toggle as “normal.”

Method 1: Change the IME default mode

1. Open Settings → Time & language → Language & region.
2. Click 日本語 in the languages list.
3. Click Language options.
4. Find Microsoft IME under the Keyboards section. Click the three-dot menu next to it and choose Keyboard options.
5. Click General.
6. Find Default input mode (デフォルト入力モード). Change to Hiragana (ひらがな).
7. Close Settings. Sign out and back in.
8. The IME now starts in hiragana mode at every sign-in.

The setting is per-user and persists across reboots. For multi-user PCs, each user has to set their own preference.

Method 2: Set the default for all users via registry

For deploying the preference fleet-wide:

1. Open regedit as Administrator.
2. Navigate to HKCU\Software\Microsoft\IME\15.0\IMEJP\MSIME (location may vary by IME version; check for an IMEJP subkey).
3. Find DefaultMode. Set to 1 for Hiragana (0 = half-width English, 1 = hiragana, 2 = full-width katakana, 3 = half-width katakana).
4. Close regedit. Sign out and back in.
5. For machine-wide deployment, set the same value under HKEY_USERS for each user’s SID, or use a Group Policy logon script that writes HKCU.

Registry is the path for IT deployment. Manual users should use Method 1.

Method 3: Switch to per-program input method

If you want different defaults per app (hiragana for word processors, half-width for terminals):

1. Open Settings → Time & language → Language & region → 日本語 → Language options → Microsoft IME → Keyboard options.
2. Toggle Use Microsoft IME for each program on (uses per-app IME state).
3. Set Notepad or your word processor to hiragana; the IME remembers that.
4. Set Command Prompt or PowerShell to half-width English; the IME remembers that separately.
5. Switching apps automatically switches the IME mode.

This is the most flexible setup — the IME adapts to context. The trade-off is that you need to set the mode once per app before it “learns.”

How to verify the fix worked

• Sign out and back in. Open Notepad. Look at the IME indicator in the system tray. Reads “あ” (hiragana) immediately.
• Type without pressing Alt+~ — characters appear as hiragana for conversion.
• Reboot the PC. Sign in. Open Notepad. Still hiragana.
• If using per-app mode, switch to PowerShell. IME indicator changes to “A” if you previously set this app to half-width.

If none of these work

If the default reverts despite the setting, a startup script may be resetting it — check Task Manager → Startup tab for any unfamiliar IME-related entries. For users with multiple Japanese IMEs installed (Google IME, ATOK), the Microsoft IME setting only applies when Microsoft IME is active; the other IMEs have their own defaults. Pick one IME as primary and remove the others, or set each IME’s default mode separately. For very old language packs from earlier Windows versions, an in-place language repair may help: remove and re-add Japanese under Language & region.

Bottom line: The half-width default is just a setting. Change Default input mode to Hiragana in IME keyboard options and the daily toggle disappears. Per-app mode adds flexibility if you switch between programming and writing.