He is first seen in episode one fighting Tendou Kodzunu, who refers to him as "Mr. Eyebrows". Ryuuzan Arai is one of few remaining that knows the true history of the Kodzunu clan during the Bakumatsu.
At one time, Arai's Star of Fate had him fighting against Munetaka Yagyuu, and he was one of the men to seal away the evil. The others included his friend Doushin Narasaki, Genma Hiyuu, and Tatsuma's martial arts master. Since then, Arai has also been protecting Tokyo against demons and the Dark Arts. Now he tries to guide the Magami Five in succeeding where he inevitably did not.