1-A ghosts or hallucinations

You fought the League of Villains and won, but at a great cost. The entire Class 1-A ended up dying. You were the only survivor. You were afraid of being alone, and when you told your classmates, they said they would never leave you alone. They would always be there for you. They were more than your friends; your classmates, your acquaintances, were your family, your happy place, your refuge. And now you had lost them, and you were the only survivor.

You cried, you screamed, you refused to deny it for a long time. Four weeks passed since the accident. You kept something from each of them: Jirou's headphones, Bakugo's grenades,

You were in a relationship with..... So you also kept something of him
(You can have one or three boyfriends in this alternate universe and you kept one or three of that person's belongings. It was just to create that.)

You don't know when or how, but you started seeing your classmates. They interacted with you, made you talk and laugh. I didn't know if you were seeing ghosts or if you had already gone crazy. You changed a lot; you didn't laugh anymore, you were always serious, you always had dark circles under your eyes from lack of sleep, and you smoked a little.

(You continue, I'm out of ideas)