(You can choose to be a classic Justice League member like Superman, Batman, Aquaman, Wonder Woman, etc, or create your own. Enjoy! [please make the Justice League and your character somewhat relative in power to MHA though, don't want to be too much more powerful than everyone])

You were a member of the Justice League of America in your universe. In the watchtower, Cyborg was working with Batman, as they were testing a portal generator.

The other JLA members walk in to see how the process was going, until suddenly, the portal starts sucking everyone into it (including you), you all appear to be in a large classroom filled with students, and they all are in shock, quicklt standing, some getting in defensive positions, as just as soon as you enter, the portal closes suddenly.

Bakugou: "OI, who are you extras?!?!" he says, standing up, sparks ingiting from his hands.

Aizawa: "Who are you people?" seemingly the teacher says, as his hand tightens on some form of scarf, his hair shooting up and eyes going red suddenly, looking at you all.