Kojirō Sasaki appears in the Onimusha anime as a secondary character and the final opponent faced by the protagonist. He is based on the historical figure known as a legendary swordsman and the greatest rival of Miyamoto Musashi. In the anime's narrative, Sasaki was killed by Musashi in the past and is later resurrected as a genma, a demonic being, by the antagonist Iemon. However, his spirit proves too strong to be controlled or enlisted into Iemon's demon army. Sasaki's motivations are singular and focused: he desires to be the finest swordsman in Japan and to settle his rivalry with Musashi through an honorable duel. He has no interest in territorial conquest or serving any master. When Iemon commands him to mutilate Musashi, Sasaki instead severs Iemon's limbs, eliminating the distraction so that he can face his rival without interference. In terms of personality, Sasaki is depicted as a proud and independent warrior. His sense of honor as a swordsman overrides any obligation to Iemon, and he insists on meeting his opponent in single combat. His attitude reflects a single-minded pursuit of the ultimate duel. Sasaki's role in the story is that of the final antagonist, serving as the ultimate test for Musashi. His resurrection represents the culmination of the demonic forces that Musashi has been fighting against, but also brings the narrative full circle by forcing Musashi to confront his past. The confrontation between the two forms the climax of the series. The key relationship in Sasaki's arc is with Musashi Miyamoto. Their history as rivals is the emotional core of their encounter. Sasaki also has a brief but significant interaction with Iemon, whom he disables rather than obeys. Notable abilities include superhuman strength and speed granted by his demonic transformation. He is depicted with multiple arms and wields his sword with extraordinary skill, matching and challenging Musashi even after the latter has acquired the Oni Gauntlet. His swordsmanship is of the highest caliber, befitting his reputation as Musashi's greatest rival. He also displays mystical powers, such as destroying a horde of skeletal genma and collapsing a stone bridge during the battle. The character does not undergo significant development over the course of the series, as his appearance is confined to the final episodes. However, his decision to defy Iemon and pursue an honorable duel shows a sense of integrity that distinguishes him from the other demonic enemies. Sasaki's fate is left ambiguous, as he and Musashi plunge into the depths while still locked in combat, with no clear resolution shown.