Darth Raijin

Basically when Izuku found out he was quirkless out a fit of rage he uses a power nobody on Earth has seen... The Force... However this usage of The Force catches a Sith's attention that happens to be near Earth

And Basically this Sith takes Izuku and about 11 years later Izuku comes back a full fledged Sith with Powers most Sith and Jedi don't. As for Why Izuku comes back and what he's gonna do your gonna have to read to find out