honestly Momo Okarun is a perfecf couple, can't see this show with a different one as the main because that was already the new subversive idea and it'd be a waste to forget it, but it's insane how good Okarun and Jiji would look and feel together. You could replace Momo with Jiji in a the first chapter, maybe in a different setting to defend Ken from bullies, and it would still feel fresh: a bully-looking guy who's actually super nice and likes paranormal just as much as the "loser". Anime never does nerd x jock couples despite their popularity