It was during the war.

Shoto and Endeavour were trying to fight Dabi. Uraraka and Tsuyu were fighting Toga. And the rest of the heroes and pros were fighting Shigaraki, who was trying to resist All For One's control.

"I WON'T LET YOU!" Shigaraki screeched, desperately clinging to his head. You, on the other hand, pounced at him to catch him off guard but got knocked out with a fist to the face.

A few moments later. You wake up in a room, skulls lying around and a shadow before you.