Age: 14 (debut), 24 (end)
Birthdate: February 18, 1994
Blood Type: B
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.