That's pretty awesome! Wish I had this when learning the hiragana/katakana!

Two remarks : it would be nice for the divs not to move while using it. I'm not sure why but when trying to keep up the pace I was always distracted by something moving on the page. I think it is beacause your divs below with % of appearance/success was moving everything when going from a 1 digit % to a two digits?

Also, when seeing an hiragana and thinking it is a one letter such as "u" instead of "mi" the system does not really detect my "u" as wrong because it only has one character and expects two. So I can change my answer and get the correct one.