Honestly, when I read this prompt (after the moment of WTF), I was all, "...Ryoma's favorite cat toy is a tennis ball and he's a nuisance on the court." And Eiji is totally the logical friend for human!Karupin, the latest and most naturally talented tennis player.

OH. KAIDOH REALLY LIKES KARUPIN. IMAGINE THEM DATING. And Ryoma supervising by riding on Kaidoh's shoulder.