Rurouni Kenshin season 1 episode 11
Episode title: Savage Han'nya - Honorable Shikijo
Kenshin, Sanosuke, and Yahiko scramble to take back Megumi from the Kanryu residence. They are confronted by Han'nya, a spy of the Oniwaban Group. He trifles Kenshin with his martial arts skills and his "Arm-extension Spell", but Kenshin successfully conquers him when he uncovers the secret of the technique during the fight. Just when it looked like the battle was up, Han'nya removes his mask and reveals his startling true face.
