The film is set in a near future chaotic Japan. A mad scientist known as "Key Man" (Itsuji Itao) has created a virus that mutates humans into monstrous creatures called "Engineers" that sprout bizarre weapons from any injury. The Tokyo Police Force has been privatized to deal with this new threat of engineers, so a special squad of officers called "Engineer Hunters" are created to deal with them. However, unlike the average police force, the Engineer Hunters are a private :wikt:quasi-military force that utilize violence, Sadomasochism, and streetside executions to maintain law and order.