You were at Nabu Island with the rest of Class 1-A. While you guys were helping out, Izuku got a phone call.

Deku: Mhm, okay we’ll help you find him right away! A sister is missing a little brother, who’s gonna come with me!

Kirishima: I’ll go!

Bakugo: You don’t have the type of quirk to help!

An hour later you found the boy his name was Katsuma, his sister showed up and started yelling at you. Her name was Mahoro.