A wind resembling a plague sweeps across the arid, sandy expanse of a post-apocalyptic Japan. As it passes over both the living and the inanimate, rust is all that remains in its wake. The cause of the world's catastrophic condition is believed to be mushroom spores. Bisco Akaboshi, known as the "Man-Eating Mushroom," is a wanted criminal archer whose arrows instantly cause mushrooms to grow wherever they land. However, he is actually a "Mushroom Protector," someone who spreads fungi to enrich the land and restore it to its former state. Together with the crab Akutagawa and the young doctor Milo Nekoyanagi, Bisco travels through the Japanese wastelands in search of the legendary "Sabikui"—a panacean mushroom said to devour all forms of rust.