You, yes you, are a member of the Bakusquad (Katsuki Bakugo, Eijiro Kirishima, Hanta Sero, Denki Kaminari and Mina Ashido + You). You've all basically been friends since you guys started at U.A. High School.

You, Kirishima, Sero, Kaminari and Mina were hanging out in Kaminari's dorm room. Bakugo was in the bathroom or something. You fell asleep on the sofa and they decided to prank you. Kaminari's great idea for a prank was to lock you in the closet. Woo. The others agreed, so they quietly pick you up, carry you to the closet, place you on the floor and lock the door. Oh, and then Sero and Mina came up with the idea to block the gap under the door with a towel (so no one would hear you and ruin the prank), so they do that as well. Double woo.

They had kinda forgotten they locked you in there, so you were stuck in there hours after you woke up. But the worst part was that it was getting increasingly hard to breathe in there. And, you might be thinking; Oh, it's because of the fact they blocked the gap under the door, so you didn't have enough air. Wrong! Well, mostly. It was also the fact that there just-so-happened to be a gas leak right in that closet. No windows by the way. You slowly lost consciousness.

Anyway, back with the others. They finally remembered you. Then they explained what they had done to a very confused Bakugo (turns out he was taking a nap), he got mad (nothing new there) and stormed off to the closet. He unlocks the door, pulls the towel blocking the gap at the bottom away then yanks the door open. As soon as he does that, you flop into his arms, very barely conscious. At first they thought you were just joking around, trying to get back at them. Until they noticed you, y'know, weren't really moving or opening your eyes. So they thought you fell asleep again. Then Bakugo noticed that the air coming from the closet was heavy and smelt a bit weird... Then it hit him; there was a gas leak. And you were stuck in that tiny closet with no access to fresh air where it happened.