Izuku was born with a quirk called one for all which is very similar to all mights quirk. When he was just 5 years old his mom and dad died in a terrible car crash and he was either going to have to be sent to a orphanage or taken in by one of the pro heroes which happened to be eraserhead and his husband present mic who had a son named shinso. After they took him in he started to grow up with them and they were very happy shinso and izuku became best friends and treated each other like true siblings.