Onimaru commands a five-member mercenary band operating in the chaos of Japan's Onin wars during the Muromachi era. Each warrior possesses a distinct specialty: Bo masters demolitions, Saru exhibits extraordinary agility, Osamu serves as the tactician, and Kiri wields her sword with skill. They sell their combat prowess to the highest bidder. During one mission, Onimaru rescues Princess Aya, who subsequently joins their ranks and develops romantic feelings for him. Onimaru and his comrades all share a history as war orphans, a past that forged their current mercenary path.

Their physical appearance is markedly distinctive, featuring highlighted hair, face paint, and eyeliner. This aesthetic creates a visual impression reminiscent of a punk rock band rather than typical medieval mercenaries. As the group's leader, Onimaru bears responsibility for critical mission decisions, coordinating the unique skills of his specialists during combat and strategy. Princess Aya's integration into the group alters its internal dynamic, introducing new interpersonal complexities. His background as a war orphan contextualizes his mercenary life. Throughout their experiences, Onimaru encounters situations demanding adaptation, particularly regarding Aya's presence and the moral weight of their violent profession.