Learn Japanese kanji from your lock screen.
A new kanji every time you wake your phone — the character, how it is read, what it means, and a word that uses it. No app to open, no streak to keep.
The card itself is deliberately plain, so it sits under your clock without fighting it:
駅 eki・えき
station
駅前・in front of station
Setting up takes three steps, and both surfaces are optional:
The last image is the live wallpaper itself, drawn by the native renderer — that is what you see behind your lock screen.
- 419 kanji across JLPT N5, N4 and N3, each with its reading, meaning, and an example compound — bundled in the APK, so nothing is downloaded.
- Lock screen and home screen, from one setting.
- Rotation you choose — a new kanji on every unlock, or on a timer from 15 minutes to once a day.
- Your own photo, GIF or animated WebP as the backdrop, plus seven built-in gradients, with adjustable dimming. Animation is capped and pauses whenever the wallpaper is not on screen, and can be switched off entirely.
- Full control of the card: text colour, size, alignment, position, drop shadow, and which of the three lines to show.
- Decks and progress — pick your levels, favourite the ones you want to see more of, mark the ones you know.
- Completely offline. Shibu declares no internet permission at all, so it cannot phone home even by accident.
Grab the APK from the latest release and install it. Android will warn you about installing outside the Play Store — that is expected for a sideloaded build.
Two APK flavours are published:
| File | Use it when |
|---|---|
shibu-<version>-arm64.apk |
Any phone from the last several years. Smallest download. |
shibu-<version>-universal.apk |
You are not sure, or you are installing on an emulator. Works everywhere. |
Requires Android 7.0 (API 24) or newer. 1.0.0 was verified on a Motorola Edge 50 Fusion running Android 16.
This is the part worth understanding before you file a bug.
Android has no public lock screen widget API on phones. It was removed in
Android 5.0, and the version that returned in Android 14 is tablet-only. The
iOS apps that inspired Shibu use WidgetKit, which simply has no Android
counterpart.
So Shibu draws onto your wallpaper instead. The system paints the same wallpaper surface behind the lock screen and the home screen, which means one live wallpaper covers both — on every Android version, with no root and no accessibility permissions.
┌──────────────────────────────┐
│ assets/data/kanji.json │
│ 419 entries, in the APK │
└───────────────┬──────────────┘
│
┌───────────────▼──────────────┐
│ RotationEngine │
│ decides which card is due │
└───┬──────────────────────┬───┘
│ │
┌─────────────▼────────┐ ┌──────────▼───────────┐
│ ShibuWallpaperService│ │ ShibuWidgetProvider │
│ lock + home screen │ │ home screen widget │
└─────────────┬────────┘ └──────────┬───────────┘
│ │
└──────────┬───────────┘
│
┌──────────────▼───────────────┐
│ CardRenderer │
│ one Canvas layout, so both │
│ surfaces look identical │
└──────────────────────────────┘
The home screen widget is a normal AppWidgetProvider and works on its own if
you would rather not change your wallpaper.
Android does not deliver ACTION_USER_PRESENT to manifest-declared receivers,
and Shibu will not run a foreground service just to watch your screen. The
wallpaper engine, however, is told when it becomes visible — which is exactly
the moment the lock screen appears. That is the signal Shibu uses.
If you use the widget without the wallpaper, choose a timed interval instead. The app says so on the settings screen rather than silently doing nothing.
WorkManager will not run a periodic job more often than every 15 minutes, and Doze can delay it further. Shibu runs a 15-minute heartbeat that checks whether your chosen interval has elapsed, so a card can appear up to 15 minutes after it was due. Shorter intervals are not offered, because they would be a promise the platform will not keep.
git clone https://github.com/Rohan3280/shibu.git
cd shibu
flutter pub get
flutter build apk --releaseYou need Flutter 3.44+ and JDK 17. The release build falls back to the debug
signing key unless android/key.properties exists, so a fresh clone builds
without any secrets.
To sign your own release build, create android/key.properties:
storeFile=upload-keystore.jks
storePassword=…
keyAlias=upload
keyPassword=…| Path | What lives there |
|---|---|
lib/models/ |
Kanji and the settings value type |
lib/services/ |
Deck loading, the method channel, the app-wide controller |
lib/screens/ |
Today, Browse, Style, Settings, onboarding |
lib/widgets/ |
The Flutter port of the card, and the lock screen preview |
android/…/render/ |
CardRenderer — the Canvas layout both surfaces draw |
android/…/wallpaper/ |
The live wallpaper engine |
android/…/widget/ |
The home screen AppWidgetProvider |
android/…/rotation/ |
When the card changes, and the background heartbeat |
assets/data/kanji.json |
The deck, read by both Dart and Kotlin |
tool/icon/ |
Regenerates the app icon |
CardRenderer.kt draws the real card onto a Canvas; KanjiCard draws the
in-app preview in Flutter. They are separate implementations of one design, and
their size constants mirror each other. If you change one, change the other.
The same applies to the deck shuffle: DeckOrder exists in both Dart and
Kotlin because dart:math's Random and java.util.Random are different
algorithms, and a mismatch would make the app advertise a different kanji from
the one actually on your lock screen. test/deck_order_test.dart pins both to
goldens produced on the JVM by tool/verify_deck_order/.
flutter test # unit and widget tests
flutter test --update-goldens test/screenshots.dart # re-render docs/screenshots/rendered/The images at the top of this README are captured from a real device. The renderer above is a fallback that draws the same screens straight from the widget tree, for when no phone is to hand.
Shibu has no internet permission. It stores your settings in
SharedPreferences and, if you pick one, a copy of your chosen backdrop in its
own private storage. Nothing leaves the device.
Full policy: https://rohan3280.github.io/shibu/privacy.html (source: PRIVACY.md)
Bug reports and kanji-data corrections are very welcome — see
CONTRIBUTING.md. The dataset is hand-checked but 419 entries
is enough for mistakes to hide in, and test/kanji_repository_test.dart will
catch structural ones.
The lock screen card layout is modelled on Moji Widgets for iOS, which has no Android version. Shibu is an independent implementation, not affiliated with it.
MIT.