Hyakutaro Senju commands the Adachi Tribe as their leader and ace pitcher. The Tribe exhibits a wild, stubborn biker-gang persona from their base in an old enclosed Adachi ward shopping arcade. He employs custom heat-generating XB gear—specifically the Fire Ball and Fire Bat—to overwhelm opponents through raw power and unwavering resolve during Extreme Baseball matches. Hyakutaro treats XB as a definitive conflict between Tribes, crushing without mercy those who display hesitation or incomplete dedication to the contest.

Though leading a biker-focused Tribe, he lacks a motorcycle license and travels exclusively by basic bicycle, contrasting with his Tribe members. His familial background includes a younger brother, Hyakuichitaro Senju, who is a new playable character in the Tribe Nine game.