It'll only show the furigana if you didn't know the kanji to begin with. So if you have already studied that kanji (in this case, 上) or marked it as known, it's not going to show the furigana because it wants you to recognize and understand the kanji.
It'll work for example with...上達(じょうたつ). If you only know the first kanji, it'll show that in kanji, and the second will be kanji with furigana.
I'm still thinking about the best way to present all this info so the feature makes the most sense, but it still needs a good bit of work.
It makes sense, but it's a bit overwhelming in the beginning.
In my case, I gathered a list of the 30 or 40 Kanji's I encountered the most in my trip in Japan and decided to study them once all in a go, so it replaced a lot of furigana in many words I know.
Why not allow to configure at which level of proficiency in a kanji does the furigana stop showing up?
People could configure that it'll stop as soon as you study it "same as now", and they could configure that at level 6 of proficiency or 9 "random levels", it'd stop showing furigana.
Another idea I have in mind would be to have the ability to toggle furigana on click? Although that might be a bit more of a crutch, so you could lower the percentage awarded towards mastery?
That's another layer of complexity that I am not sure most users will benefit from (alongside the frustration/confusion that comes with any extra layer of settings).
I do not plan on adding furigana to click - it's a quiz system, so you either know it or you don't. The mastery system doesn't allow "slices" of mastery like that, and in the end, the learner couldn't recall the kanji, so at least for that study vector, they were not able to recall it (woo, that was a lot of commas).
