Age: 14 (debut), 24 (end)
Birthdate: February 18, 1994
Horoscope: Aquarius
Blood Type: B
Height: 171cm
Weight: 58kg

Mashiro is a 14-year-old boy who doesn't know what to do with his life. One day his classmate Takagi finds out about his amazing drawing skills and asks him to help create a manga. He initially declines, but changes his mind when Takagi helps him get engaged with his crush, Azuki Miho.

He and Takagi create manga for Shonen Jump under the pen-name Ashirogi Muto. Mashiro is very talented in drawing although he is very dissatisfied with his style. He specializes in drawing fairly dark characters. His favorite manga is Ashita no Joe.

After Ashirogi Muto's manga "Reversi" receives an anime adaptation and Azuki Miho secures the role of the main heroine, Mashiro properly proposes to Azuki in front of her old house which he had purchased for the two to live in. The two finally have their wedding ceremony after Ashirogi Muto's next serialization.