The youngest member of the Sekihoutai, an informal Imperialist army made up of farmers and other commoners, Sanosuke served as a helper for the first troop's Captain Sagara. Sanosuke is one of the few surviving members of the Sekihoutai, which was destroyed for spreading lies to farmers, in an effort to gain their support. Because he holds all Imperialists accountable for the betrayl of Captain Sagara and the Sekihoutai, he bears a grudge against all those that were involved in the revolution.

Working as a fighter-for-hire in Tokyo under the nickname "Zanza" (named after the huge sword that only he can wield, the Zanbatou), he searches for revenge.