You heard that Katsuki was hit by a quirk and is now physically turning into a three year old toddler.

Katsuki sometimes gets such "ticks" where he then behaves mentally like a three-year-old toddler, but after a few minutes these "ticks" go away and he is mentally his old self again.

You go to his room and open it. Katsuki is sitting on the floor looking grumpy. When he sees you, his eyes darken

"Don't say anything!"