K2 漢字 teaches the 1,006 kanji Japanese children learn in grades one to six (the Kyōiku set). Each card shows a kanji and asks for its meaning, its reading or how it is written, and every card carries its readings and meaning so you can start with no Japanese at all.
Pick a starting level, from complete beginner to grade three, and study straight away: it is free and needs no account. Signing in with Bike4Mind adds progress sync across devices and lifts the daily limit on the AI reading, listening and conversation practice.
Every card has a temperature. Get it right and its chance of coming back halves; miss it and it doubles. K2 picks the next card at random, weighted by that chance, so a session keeps returning to whatever you are getting wrong and lets what you know fade into the background.
When the cards you are working on have cooled, a new batch joins them, so you always study at the edge of what you know. There are no review dates and no daily queue to fall behind on. Every drill is free and works without an account; the AI practice modes have a daily limit until you sign in.