Legend tells of two civilizations besides the human race reigning over Earth: the Makai demons and the Juujinkai, a strange hybrid of human and beast. Every 3,000 years, a supreme Overfiend named the "Choujin" emerges to balance the three realms of Earth. In contemporary Japan, Amano Jyaku, a Juujinkai, has spent 300 years scouring the land and finally locates the Choujin inside a school slacker named Tatsuo Nagumo. Amano, accompanied by his sister Megumi and sidekick Kuroko, must now protect Nagumo and his girlfriend Akemi Ito from the Makai, who perceive Nagumo as an evil being set on obliterating all life on Earth instead of the Choujin.