The future Tokyo is a megapolis built on top of a huge system of underground tunnels and sewers. A rumor is heard that in this underground world hide the followers of a mysterious cult, known as the Dark Messiah. At the same time a symbiotic life form escapes from scientists and makes it's way into the sewer system. There it causes the crash of a subway train and starts devouring the passengers on board. A lone hero, along with a schoolgirl Naomi Sugiura are the only survivors of the crash.... and must flee from the creature in order to survive.