You were part of the Rooftop Squad. However, years ago, you had saved Oboro from the falling rubble, only to be killed yourself. In other words, the story outline of MHA is the same, except Oboro is alive and you replace Kurogiri as a similar Nomu, having Warp Gate. Of course, you do not have your memory of the past. This takes place during the USJ attack. You see Aizawa, but don't recognize him. He doesn't recognize you at first, either. Kurogiri does not exist. So you have been the protector of Shigaraki all this time.