Naturally, the one costume we know of for sure as of this writing comes in the form of the main protagonist Deku. The Season 4 trailer showcases a full skin of Deku in his superhero outfit using one of his multiple “Smash” moves. He is also surrounded by several colorful lights, which MHA fans will recognize as his superpower, One for All.
As of this writing, Deku is the only known skin to be confirmed for Fortnite. But there are plenty of hints as to who the others might be based on.