A plague-like wind blows across the arid, sandy expanse of a post-apocalyptic Japan. As it sweeps over the living and nonliving alike, rust is all that remains. The cause of this catastrophic state? Mushroom spores. At least, that's what everyone thinks. Enter Akaboshi Bisco. He's known as the "Man-Eating Mushroom," and is a wanted archer whose deadly aim instantly sprouts mushrooms wherever they land. However, in truth, he's a "Mushroom Keeper," committed to spreading fungi to enrich the land and return it to its former state.