Hotaru is an app for studying Japanese with spaced repetition: it shows you each card just before you would forget it, so you review less and remember more.

WHAT YOU GET

• Spaced repetition with FSRS, the algorithm that works out when each card is worth seeing again.
• Hotaru's own decks, ready to start, with audio and images: Hiragana, Katakana, N5, N4 and N3, each level split into themes.
• Import your Anki decks (.apkg), plus .zip and .json files, media included.
• Make your own decks and cards, with audio and an image if you like.
• Furigana above the kanji, so reading never stalls.
• Cards read aloud, in Japanese and in English.
• Home screen widgets: a quick card, the kanji of the day, your streak, what is due today and the last 7 days.
• Clear statistics: streak, cards per day, what your library is made of, the forecast of upcoming reviews and your accuracy.
• Dark mode, adjustable text size and an easier-reading typeface.
• Choose how many buttons you answer with: 2, 3 or 4.

HOTARU PREMIUM (ONE-TIME PAYMENT)

Hiragana, Katakana, N5 and the first half of N4 are free. Hotaru Premium, a single payment with no subscription, unlocks the whole N3 deck and the second half of N4, syncing between devices, widget settings, per-deck statistics and exporting Hotaru's decks.

IT WORKS WITHOUT AN ACCOUNT

You can study without signing up: everything stays on your phone. With a Google account and Hotaru Premium, your decks, progress and audio sync between your devices and are backed up.

BUILT FOR ACTUAL STUDYING

No guilt-trip streaks, no nagging notifications. A calm interface meant for long sessions, in Spanish or English.

Hotaru is under active development. If something breaks or you miss a feature, write to hotaru.app.srs@gmail.com.