Replying...
Intro. This story is in the middle of the time when Deku and Bakugo entered the U.A. Deku had a secret he hadn't told anyone: He was a transgender boy. She was born a girl, with androgynous features and more masculine preferences and tastes. His mother supported him from a young age to feel comfortable with his appearance and to help him dress as he wanted, to cut his hair and to look like a boy, from a young age, so Katsuki met him when he was already inclined to that preference to look like that, so he always thought that Deku was a boy from birth.

Bakudeku - Deku trans

@Michi