A cataclysm has devastated Japan, leaving only endless sandy wastelands, while a strange oxidizing affliction haunts the last remnants of society, turning life into ruin everywhere forever. The authorities claim that this new reality stems from fungal spores spread by figures like Bisco Akaboshi, dubbed the 'Man‑Eater Mushroom,' in the aftermath under dawn. Yet Bisco contests this view firmly steadily with resolve. In truth, he is a 'Fungus Guardian,' determined to find the legendary 'Sabikui' mushroom—believed to be the ultimate cure for the corrosion sickness in distant hills. He is joined by his colossal crab Akutagawa and the compassionate doctor Milo Nekoyanagi, who seeks a cure for his ill sister across the coastal towns. Despite commoners' suspicion, Bisco persists in his mission to cleanse the decaying world with unwavering resolve against all odds.
