TV-Series
Description
Okada Izō, also known as Hitokiri Izō, was a historical samurai of the Tosa Domain during Japan's Bakumatsu period. He stands as one of the era's four great hitokiri (manslayers), alongside Tanaka Shinbei, Nakamura Hanjirō, and Kawakami Gensai. His early training occurred under Takechi Zuizan, covering multiple sword styles like Ono-ha Ittō-ryū, Kyōshin Meichi-ryū, and Jikishi-ryū, though he frequently left dojos before mastering them. His swordsmanship was described as "indomitable and nimble in fencing as a falcon."

Izō joined the imperial loyalist group Tosa Kinnōtō. Under Takechi's command, he assassinated political targets such as Honma Seiichiro, government officials, and police sergeants, framing these killings as "divine punishment" (天誅, Tenchū). His rough temperament eventually caused a rift with Takechi, leading to his expulsion. Later, through Sakamoto Ryōma's mediation, he served as a bodyguard for Katsu Kaishū, successfully thwarting assassination attempts. His life descended into debt, alcoholism, and homelessness after being abandoned by allies.

Arrested in 1865 for assassinating Tosa regent Yoshida Tōyō, Izō endured torture and confessed to multiple killings. He was beheaded on May 11, 1865, leaving a death poem lamenting futile loyalty. Historical records note comrades considered poisoning him to prevent further confessions, but Takechi intervened.

Fictional portrayals expand upon his core traits. He boasts of his swordsmanship, viewing others with contempt yet harboring deep insecurities. His personality is rough, impulsive, and violent, especially when mocked. He intensely resents Sakamoto Ryōma, once a close friend, seeing Ryōma's actions as betrayal—a grudge persisting even as Servants. Despite his aggression, he demonstrates loyalty when treated earnestly, though his lack of intelligence makes him easily manipulated.

His abilities focus on swordsmanship genius. As an Assassin-class Servant, he wields a nameless katana. His Noble Phantasm *Shimatsuken* allows him to replicate any witnessed sword technique, excluding those tied to Noble Phantasms or non-Anti-Unit classifications. Skills include *Presence Concealment* for stealth, *Manslayer* enhancing lethality against humans, and *Eye of the Mind (False)* for danger intuition. These make him exceptionally effective against humanoid opponents despite low mana and luck parameters.

Relationships are complex and conflict-driven. He despises Ryōma, Shinsengumi figures Okita Sōji, and Hijikata Toshizō, viewing the latter as hypocrites. His dynamic with Ryōma's wife, Oryō-san, is contentious but non-hostile. In *Fate/type Redline*, he tortures a master for information, displaying brutal pragmatism. In *Like a Dragon: Ishin!*, his devotion to Takechi borders on obsession, fueling jealousy over Ryōma's bond with Takechi. This leads to multiple duels with Ryōma, ending in Izō's death and a plea for Ryōma to stop Takechi's destructive plans.