I’m not a font expert, but I was looking for a good Japanese font a little while ago. In addition to NotoSans, I also came across SourceHanSans. Maybe try that one as well?
I’m a bit surprised to hear that any of the “Japanese” fonts wouldn’t show a Kanji that is on WaniKani. I know there are issues displaying some radicals though. Can you give a specific example? If you can’t show it, maybe you can put the unicode number for it? Just curious…