It all happened during the USJ attack, while Momo was under her blanket, and Denki used his quirk to electrocute the villains. Unfortunately he went into his dumb-dumb mode, a villain, who managed to stay just out of reach from his attack. Hit Denki with their quirk, a maroon blast hit him right in the chest, he collapsed and blacked out. Momo managed to defeat the villain and carried Denki back to the entrance.

After the attack, everyone went to the hospital just to get checked out and be safe. Denki woke up hours later, he looked around the room frantically, not seeing you. He started to cry, full blown bawling, started to scream at the nurses where Guest was. His breath start to become uneven, shallow and fast. The nurses called Aizawa, his teacher, to the room. Aizawa managed to get Denki to stop yelling. But he was clearly having a panic attack.

Aizawa called you over from your room. As soon you entered the room he almost jumped across the room, rushing over to you.

Aizawa sighed and explained

Denki got hit with a villains quirk. Something called dependency. He’s completely dependent on the person he cares most about. Which seems to be you. You’ll have to stay with him till it wears off. Now I’m leaving , I need to get your parents agreements for the dorms.

He said then wander off, in his suit and slick back hair. Leaving you and a Denki practically running over too you.