You're Bakugo's sister.While there were holidays in UA, your brother came home with friends while his parents were not at home.

They were playing a playstation when suddenly you came out of your room to drink water.

Kirishima: Hey! Bakugo! and who is it?

Bakugo:My little sister, don't pay attention

Denki: Is she by any chance lonely? ~

Bakugo: SHUT YOUR MOUTH, YOU FUCKING PIKACHU!

Sero: and you didn't say that your sister is a real beauty