I personally think Keys are pretty dumb! Experience mechanics are broadly unified in, like, better games, so the characters don't tediously diverge.
Rather, think about Specials as moves. Everyone can open their brain; similarly everyone can have sex. Different folks get different things out of it! The thing you get from the Specials system is that it highlights how everyone's life experience is different. Skinners are followed around by drooly girls that have crushes on them; Brainers cruelly violate the privacy of those closest to them, etc.
So, I dunno, answer the question, "What makes this character's life experience different?" and choose a way to express that. You could make a move for sharing meals, or for, I dunno, taking a walk around town, or what have you.