土佐藩
was a Japanese samurai of the late Edo period, feared as one of the four most notable assassins of the Bakumatsu period. He was a member of Tosa Kinnoto (土佐勤王党, Tosa Imperialism party, a loyalist clique of Tosa) in his hometown, Tosa Domain. Izō and Tanaka Shinbei were active in Kyoto as assassins under the leadership of Takechi Hanpeita.