Hm, competitive wanikani? Could be like some territorial-type game, but combat consists of choosing a wanikani item from the other person’s supposedly-learned list and challenging them with it. If they can’t answer, they are defeated. If they answer it correctly, they challenge you back with one of yours.
You would also gain territory or points or whatever by learning more kanji, so you have to balance wanting to do more, more, more, with having to know them well enough to fend off challenges.
Ooh, and the items would not be all equal points. If you miss one, the other person gets points for not only that one, but all the ones that depend on it later. So you could challenge someone with a radical and get credit for all the kanji using that radical if they don’t know it. On the other hand, they’re more likely to know the earlier ones and radicals, leaving you more likely open to counter-attack.