Okamoto Katsushiro is a young and inexperienced samurai who wishes to be Kambei's student, calling him sensei almost from their first meeting. He idolizes the principles of bushido. He promises to protect Kirara no matter what, and seems to be attracted to her. He grows stronger and more skillful throughout the series, eventually becoming a worthy student of Kambei; and he also comes to terms with killing enemies, after reacting in shock the first time. He becomes strong enough to deflect the capital's main cannon, and defeated numerous bandits all by himself. He gains emotional strength as well, and understands what his true reason for becoming a samurai is. After turning down Kirara in the end, he explains to her that he intends to continue his life on the battlefield. After hearing this, he receives Kambei's sword from him in recognition as his student.
He is the fifth samurai, and the second one to offer to join.
Comparison to the movie
Unlike in the original movie, Katsushiro shows more focus on becoming a samurai and improving his skills greatly in the anime, whereas in the original he was preoccupied with a love affair. As opposed to the movie however, he doesn't fall in love with Manzo's daughter Shino, but the MikumariKirara.