Age: 10

Birth Place: Harima Province

Class: Year 1, Class Ha

Committee: Biology Committee

A bright and friendly boy who almost always has a smile on his face. His father is a yamabushi and training with him in the mountains has made Sanjirou quite perceptive as well as a fast runner. Among his classmates only Rantarou is faster, and because of it they have an ongoing friendly rivalry.

Like his roommate Heidayuu he's fond of traps, and their room is full of traps and devices they've set up.