Sanosuke, formerly the fighter-for-hire Zanza, gives up mercenary work after his encounter with Kenshin made him realize how he was just fighting to calm his anger. He later becomes Kenshin's most trusted friend, and discovers a different kind of strength.
"Sano's strength isn't only in his fists. For the sake of those he wants to protect... He's holding on to the belief that he can't lose."