A young samurai who, until fighting for the Kanna village, had never been in a true battle, but always believed in the honor of the samurai code. He wishes to become Kambei's student, and promises to protect Kirara no matter what. He first meets the villagers when a thief attempts to steal their rice in the city, but Kirara initially has doubts about his skill because he does not have the "scent of battle" on him. However, Katsushiro gains steadily in skill throughout the series: at the outset he cannot defeat a simple thug and is beaten by a single blow, but by the end he can defeat numerous Nobuseri at once, deflect an enemy beam cannon shot with his sword and lead the villagers in their successful defense against the capital.
Of the samurai, Katsushiro's character evolves the most throughout the series. At first he is overcome with shock upon his first kill. Kirara is overcome with guilt for having brought him into a situation in which he is forced to take life, and pledges to support him even as he falls into darkness. Kambei and the other samurai soon teach Katsushiro that taking life is part of being a true samurai. By the last battle he can kill numerous enemies without flinching. Katsushiro takes a liking to Kirara early on in the series, attempting to protect her in numerous situations, and at one point asks her to come with him after he has a falling out with Kambei. He later returns to Kanna village after his solo journey as a much more mature and skilled samurai.
Katsushiro is one of the 3 surviving samurai following the final battle against the capital, and is shown post-battle to have gained significant wisdom and maturity from his experiences. His skills are improved enough by the end that Kambei even shows great respect towards him, and presents Katsushiro with his own katana. In the end he leaves the village to continue his samurai life.