Mirio Togata - Boku no hero - Everything you need to know

Mirio Togata, also known by his hero name Lemillion  is a student in Class 3-B at U.A. High School and is part of The Big 3.
Before Izuku Midoriya, Mirio was the top candidate for All Might's successor and inheritor of One For All.

Mirio normally comes across as extremely goofy and very energetic with some peculiar habits. Going solely based on his personality, many tend to question how Mirio is U.A.'s top student. Mirio has a very optimistic attitude and is also almost always smiling. His personality is what led Sir Nighteye to believe that he could be the man to replace All Might as the symbol of peace.

Mirio does not allow his laid back nature to cloud his judgment or impede his dreams of becoming a hero. He has proven to be an extremely hard worker, turning a near-unmasterable ability into one of the world's most powerful Quirks. Mirio is constantly looking for ways to improve his skills and tries to work toward his goals by accumulating different experiences to learn from them.

 Like many young men and women, Mirio was inspired by All Might to become a hero. Knowing he can't rescue everyone, Mirio chose the hero name "Lemillion" because he aspires to be a hero who can save over one million people. Despite Mirio's uplifting personality, he can suffer from failure just like everyone else. He has an excellent understanding of hero protocols and controlling his emotions in order to see the bigger picture.

Mirio's Quirk allowed him to become intangible, letting him travel through solid walls and the ground while also letting enemy attacks harmlessly pass through him. If he returns to his solid state while phasing through something, his body would be repelled outward.

While intangible, he experiences a falling sensation because he still has mass, and everything passes through him, including light, sound, and air; meaning, while his Quirk is active, he can't see, hear, or breathe.

Mirio lost his Quirk after his fight against Kai Chisaki, during which he was struck by a bullet containing the Quirk-Destroying Drug, taking the bullet in Eri's place. However, according to Shota Aizawa, once Eri gets a better handle on her reversing Quirk, Mirio's own Quirk will be restored.