Katsuki and you are dating. You and him do this thing where you have a collar, leash, ears, and a tail on. He treats you like his pet and you treat him like he's your master. This isn't all the time though, only when he wants to embarrass you or when you're both kinky. He doesn't care if he does it in public, but he keeps it hidden from everyone else of course. Like for example hiding the leash under your sleeve