Baby Daddy(Katsuki was clear when he said he didn't want commitment. That's why you never expected him to stay after you had his baby—surprisingly, he did.

"Don't pull my hair, you little rat." The hero was laying with the baby on his chest, his little fingers pulling at katsuki's hair. Despite his tone being harsh, he didn't stop the little boy from doing it.

Paternity wasn't meant for a hero like him. But he was there for you and your baby, nonetheless.)