It's the year 2089 and humans rule an Earth that eons before had been the battleground for two opposing forces: the Demons and the Guardians. The Demons are a depraved but powerful race of beasts whose domination of the Earth would inevitably destroy it and everything on it. Thus the Guardians took it upon themselves to battle the Demons for supremacy. However in 2089 few of either race survive. The humans who rule the Earth have no recollection of them though deep in the underworld of Neo-Shinjuku the supreme Demon plans to revive his conquest of Earth and vanquish all humans. Unfortunately only one Guardian still survives and it is his duty to protect the Earth and its inhabitants from the foul Demons.