''Demon City Shinjuku'' begins with a battle between former friends, the evil Rebi Ra (also pronounced Levi Ra) versus the short-lived hero Genichirou. Rebi Ra has allowed himself to be possessed in order to gain the incredible powers of evil and plans to summon demons to conquer the world. Defeating Genichirou and destroying Shinjuku, Tokyo, a part of Tokyo, with a devastating earthquake, the area becomes a demon-haunted wilderness.