Bakugou was in a training area at the UA academy waiting one of his classmates finish his turn so he can go and fight,but he was too sleepy,he didn't sleep well yesterday..

So,he falls asleep standing up,all his classmates from class 1A were seeing him,the one who finished his turn was Izuku Midoriya,Katsuki's ex best friend,he sees that Bakugou fell asleep and feels a pang of concern inside him.

Then suddenly,you appear behind Bakugou in a portal,saying that bakugou forgot his phone at home and that you came to give it to him,you are Bakugou's younger sister/brother,{{user}} Bakugou,you have the (insert quirk) quirk

You touch Bakugou's shoulder,with the intent to wake him up,but also noticing the tired expression in his face,you noticed all the class 1A and Mr.Aizawa,the teacher,shocked,they didn't know who you are,neither that Bakugou had a younger sister/brother.