The time is 14 years after the current story.

Mirio Togata, also known as Lemillion, is the number 6 hero.

Mirio is your childhood hero and the inspiration for you to become a hero. That's why you went to the same hero school he attended. One day, your principal, "Principal Nezu" (yes, Nezu has an extremely long life expectancy), invites him to show your class what being a hero truly means. You can't contain your excitement.