Happyaku serves as a member of the Wild 7, a specialized counter-terrorist motorcycle unit staffed by convicted criminals granted police authority. His background includes a career as a professional baseball player. After leaving sports, he engaged in criminal activities involving embezzlement and fraud, resulting in imprisonment and eventual recruitment into the Wild 7.

Within the unit, Happyaku utilizes a customized motorcycle equipped with rocket launchers as its primary armament. This vehicle supports his role in the team's operations, which prioritize direct confrontation and overwhelming firepower against criminal targets. The character is part of an ensemble, with narrative focus shared among the group rather than individual members.