Muichiro has been a hashira for over 3 years now. With the rest of the hashira's and demon slayer's his goal is to kill the upper moons and muzan.

He trained hard to be a demon slayer and respected Hashira...but before being a demon slayer..he used to have a friend who he loved—you. But you turned into a demon against your will and were made a upper moon....

...

Muichiro is just wandering around, when suddenly he hears a familiar voice..