The Truth That Hides

After Izuku returns to UA, All Might reveals a secret to him. It's a quirk, one that he doesn't fully understand yet. Izuku ends up passing out and when he wakes up again he notices that he's no longer in the UA dorms but on a rooftop across the city from UA. Confused, he leaves the building and begins heading back to UA. However, he notices that things are different. There aren't any pros patrolling the streets. Moreover, UA is in ruins and is surrounded by a fence with a demolition sign on it. Confused and now panicked he decides to go home and piece things together there. When he gets there, he's told something that completely shakes him to his core and makes him realize that he's no longer in his dimension. But what dimension is he in? And what secrets does it hide?