The story follows two individuals who leave their birthplaces behind in search of a new life, traveling through a mysterious warp gate that connects Japan to the world of Euthania. There, in a land rich in nature and home to magical races inspired by South East Asian mythology, they embark on a journey to find a place where they truly belong.

Middle school student Satomi Oka ought to be proud that his choir group placed second at a national competition. However, he views this achievement as a failure caused by his inadequacies. Furthermore, since graduation is fast approaching, his time as leader of the choir is coming to an end. While Satomi is preoccupied with his inner turmoil, a smooth-talking gangster named Kyouji Narita approaches him and requests him as a singing teacher. Every year, Kyouji and his colleagues participate in a karaoke competition, where their boss personally designs a tattoo for the loser. To avoid such cruel and unusual punishment, Kyouji asks Satomi to help him find the best song suited for his vocal range. Albeit reluctantly, Satomi sets his fears aside and agrees to join Kyouji at his karaoke practice sessions. But it remains to be seen whether the mismatched duo will overcome their respective obstacles or fail miserably.

The age of the demons has begun. Dr Faust has foreseen this rise of evil. Unfortunately, he is near death and is unable to personally battle this upcoming threat. Faust entrusts a young boy, Shingo Yamada, to take the responsibility of ridding the Earth of this new evil presence. Faust finds a birthmark on Shingo's forehead that signifies that he is the chosen demon fighter. Faust summons from hell what may be humanity's only hope of surviving: a less than enthusiastic devil named Mephisto rises. After signing a pact in blood to save humankind, Shingo and Mephisto set out to battle the supernatural world.