Bisco Akaboshi is a Mushroom Keeper, an archer whose arrows sprout mushrooms where they land, hunted across a rusted-out Japan under the bounty name "Man-Eating Mushroom." He crosses the iron desert with the young doctor Milo Nekoyanagi in search of the Sabikui, a mythical mushroom rumored to cure the rust disease eating away at his dying mentor Jabi. This light novel is the original source for the Sabikui Bisco manga and anime adaptations.