Kyodai Ken (sometimes spelled Kyodai-Ken, Japanese for "Giant Fist" or more simply called "The Ninja"") is a fictional character who has appeared in two episodes of Batman: The Animated Series. He was voiced by Robert Ito.
Kyodai Ken was an aspiring thief who used to learn martial arts under Yoru Sensei in Japan. Kyodai would always defeat fellow student Bruce Wayne in combat and teased Bruce by calling him a "pampered rich boy". But one day Bruce once caught Kyodai attempting to steal one of Yoru's swords, and Yoru expelled Kyodai from the martial arts dojo as punishment. Kyodai swore revenge on Bruce Wayne.
Kyodai eventually comes to Gotham City in the episode "Night of the Ninja". In this episode, Kyodai, disguising himself in generic ninja garb as well as employing natural ninja stealth tactics and gear, commits several robberies on Bruce Wayne's properties. At one point he briefly fights the Batman, but Kyodai escapes the battle. Later on, Kyodai kidnaps Bruce Wayne and reporter Summer Gleeson (who happened to be with him at the time) to settle once and for all who is superior. Bruce manages to defeat Kyodai, who disappears into a river. It is later revealed that since Kyodai battled Bruce in both of his identities, Bruce Wayne and Batman, he was able to deduce that they were the same person.
Although originally intended as a one-shot character, Kyodai eventually made a return appearance in the episode "Day of the Samurai". In this episode Kyodai returns to Japan and kidnaps Yoru's star pupil, Kairi, and holds her hostage. In return Kyodai wants Yoru to divulge the secret hiding place of the ancient scrolls containing details about a forbidden martial art. Yoru calls in Bruce Wayne to help battle Kyodai, who confirms that he knows about Bruce's secret identity as Batman. Kyodai eventually gains the scrolls and masters the Ohinemuri death touch, a move he intends to use on Bruce.
Kyodai lures Batman to a final battle along the slope of an active volcano, once again with use of a hostage. This time the hostage is Bruce's own butler, Alfred Pennyworth. During this battle, Kyodai tries using the death touch, but it fails as Batman had discovered the area that needed to be touched and was able to shield it (although Kyodai was initially unaware of this as Batman feigned falling victim to the death-blow in order to buy some time). The battle ends when Kyodai is stranded on a rock in the middle of a flow of lava. Batman tries to save Kyodai, but Kyodai refuses Batman's aid and disappears in the following explosion. He is presumed dead.