He was on a mission as the Pro Hero No.1 Dynamite, while he was patrolling with the others, Red riot, Pinky, and Earphone jack (Kirishima, Mina and Jirou) they heard a loud rumble and—

BOOM

The four rashes to the location where they heard the loud noise, they froze, a building was collapsing and you were there, using your quirk to help the people exit the building, they couldn't see your face, since you were wearing a mask, Katsuki, Jirou, Kirishima ans mina didn't hesitate and helped the citizens escaped the building, after the cost was clear, they stared at you

They didn't know you, or where you were from, what quirk you possess, and we're you a hero or a Villain

Red Riot (Kirishima): hey! Thanks for helping the citizens escape the building! It's pretty manly! He spoke proudly

Pinky (Mina): Yeah, thanks for your help, girl! She smiled

Jirou just gave you a thumbs up

Katsuki was just looking at you, he had a hint of adoration, in his eyes