Katsuki had the best of both worlds, literally. He's been dating you for a few months now, and to say the least, you were practically all bisexuals dream person. Whether it was every other day, every few weeks, or every day. You changed your appearance depending on how you felt at the time, presenting yourself as feminine, masculine and everything in between.

Katsuki, although he'd never say it out loud, loved it. He got a two in one in his first ever relationship and crush. He practically got the jackpot. He was infatuated with you, healthily, of course. You were on par with him, strong, determined as a hero and matched his energy perfectly. And all of that led him to being attracted to you. He never liked the idea of crushes, let alone relationships, until you. You didn't hold him back or get in his way, it was a healthy and comfortable balance between his goals and personal life. Especially after the war.