Japan has become a wasteland devastated by the Rusty Wind which causes all things to rust away. A suspicious looking priest visits a checkpoint all alone, yet on his back rests a bow priests wouldn't use. Meanwhile, Milo, a doctor running a clinic in the town of Imihama, is researching new medicines in secret in order to save his older sister, Pawoo, who's being corroded by the Rust. But that day a stranger appears before him...

The wanted criminal, Akaboshi Bisco, causes havoc in the town of Imihama using his bow to cause giant mushrooms to bloom. Bisco searches for a doctor who can synthesize medicine to save his mentor, Jabi, who has become gravely ill. Bisco storms into the clinic and accosts Milo, but Governor Kurokawa hears the commotion and dispatches his elite forces.