One day, a delinquent boy, Razor Eiji, sensing instinctive danger, holed himself up in the basement of an abandoned warehouse. Then, after a long rainfall, he went outside and saw an uninhabited town and the nocturnal "Worst Man" creatures, which are born from human corpses and regenerate if they are killed or dismembered. The rain was mixed with a terrifying virus that kills humans and transforms them into monsters.