Benmaru is a young boy who becomes one of the ten warriors serving under the feudal lord Sanada Yukimura. He is introduced during the group's journey when they encounter a series of traps in a forest. The boy responsible for setting these traps emerges and, impressed that they were the first to ever escape his snares, excitedly asks to join their group. Initially calling himself Rokuro, he changes his name to Benmaru after discovering another warrior already in the group bears that name; Yukimura is the one who gives him this new name.

Benmaru is associated with the element of fire, and his primary abilities revolve around the use of gunpowder and explosive devices. His combat style relies on these firebombs and other pyrotechnic gadgets, making him a unique fighter among the assembled Braves. Despite his youth, he is considered one of the ten warriors, with his role being that of a strategist and guide during battles due to his intelligence and analytical nature. In addition to his combat skills, he is also portrayed as a capable healer, using knowledge of medicine and herbs to tend to the wounds of his allies.

Personality-wise, Benmaru is often viewed as a bratty or grating child, a trait common to his young age. He is described as having a cautious and calculating demeanor, frequently analyzing situations before taking action. He is deeply loyal to his companions and protective of their well-being, showing a caring side beneath his sometimes abrasive exterior. His strategic mind makes him a reliable asset in planning the group's tactics, and he is respected by the other warriors for his contributions.

Throughout the story, Benmaru's relationships with the other Braves develop as he proves his worth in battle. He fights alongside the monk Miyoshi Seikai, at one point providing a special device that enables one of Miyoshi's punches to land effectively against a powerful opponent. He also shows a willingness to follow orders, reluctantly agreeing to wait behind when Yukimura instructs him to do so during a dangerous mission. While his introduction occurs relatively late in the series, he participates in the final conflicts against the Iga ninja, including members of the League of Five. Benmaru represents the youthful energy and tactical ingenuity within Sanada Yukimura's assembled warriors, using his intelligence and explosive expertise to support the group in their mission.