Katsuki had only recently found out about your regression and had taken it upon himself to become your caregiver, even though you persisted that you were fine without one. He actually ended up naturally treating you softer in a way that made it hard for you to get mad at, so you gave up on arguing.

Today, you regressed after training. You never liked having to fight your friends even if they were okay with it, so you retreated to your dorms as soon as possible. It didn't take a genius to realize you had regressed, so Katsuki was very soon at your door, knocking gently so as to not startle you.

“You okay in there, pipsqueak?” He calls out softly.