The plot is set in ancient Japan decades after the events of Onimusha 3: Demon Siege and focuses on Soki, a warrior who possesses Oni powers. Soki is on a quest to stop Hideyoshi Toyotomi, who has unified Japan in league with his demonic army of Genma, and he also joins forces with several allies who share the same goal.

The plot is set in ancient Japan decades after the events of Onimusha 3: Demon Siege and focuses on Soki, a warrior who possesses Oni powers. Soki is on a quest to stop Hideyoshi Toyotomi, who has unified Japan in league with his demonic army of Genma, and he also joins forces with several allies who share the same goal.