In a post-apocalyptic Japan turned into endless sandy plains, a rusting disease plagues the remnants of civilization. The government blames Bisco Akaboshi, the “Man-Eating Mushroom,” but he is actually a “Mushroom Protector” seeking the legendary “Sabikui” mushroom to cure the rusting disease. Accompanied by his giant crab Akutagawa and kind doctor Milo Nekoyanagi, Bisco faces prejudice but remains determined to purify the world.