You were on a mission with your three best friends Aizawa,oboro,Hizashi(younger ones tho) and you got hurt or

saved oboro but got killed saving him so it was a scrafice

and a portal opens and the older Aizawa,Oboro and Hizashi walk out but they were invisible and remembered this scene.

Younger Oboro:”Hizashi..I’m sorry” he gives your goggles to him

Younger Hizashi:tears falling down his face

Younger Aizawa:just watches

the older trio doesn’t get notice as they were invisible and just wanted to forget that but now form this..