Shuuji is Harima Kenji's little brother. He first appears at the Tsukamoto doorstep as a kid who supposedly ran away from home, but the truth was that he had become infatuated with Tsukamoto Yakumo and wanted to get close to her. While there, he plays some games with Tenma, all of which he wins (Tenma later calls on Yakumo to beat Shuuji at Go, which he has no idea how to play). Sometime after this incident, he helps Harima protect his animals by dressing up like them and pretending to reherse a play. Most recently, we have seen Shuuji attend the Cultural Festival with Tennouji Mio.

Shuuji is Harima Kenji's younger brother, although they don't live together.

Shuuji fell in love with Yakumo at first sight, and even ran away from home to get close to her. They represent the Go Faction. Shuuji and Mio go to the same school. Shuuji does care for Mio, even though he likes Yakumo too, as he was worried about her when she got lost during the Cultural Festival.