Set in the year 1600, during a fictionalized version of Japan's late Sengoku period, Nioh follows William, an Irish swordsman who travels to Japan in pursuit of an enemy. Amid a land torn by war, supernatural creatures known as yokai have begun to appear and spread chaos. William crosses paths with the warlord Tokugawa Ieyasu and his ninja ally Hattori Hanzo, forming an alliance against both the yokai and the Western sorcerer Edward Kelley, whose dark alchemy is driving much of the conflict. As he is trained in the ways of the samurai, William is drawn into the wider struggle to unify Japan while hunting the man who wronged him.