Katsuki got hit with a quirk during his mission. The quirk didn’t had any bad effects but it ended up splitting his personality in half. His normal self and the opposite of him, who is nice and sweet, they were talking and a bit of arguing

Katsuki: “Shut up! Stop being weak!” He yelled at the other

Nice Katsuki: “I’m not weak, your just being rude” He said softy