In a post-apocalyptic Japan ravaged by the Rust Wind—a catastrophic phenomenon that corrodes everything it touches, turning flesh and steel into dust—society lives in fear under the tyrannical rule of Governor Kurokawa of Iken. Amidst this wasteland, Bisco Akabane, a notorious criminal known as the "Man-Eating Mushroom," seeks a legendary fungus called the Rust-Eater, believed to possess the miraculous power to cure the rust and save the dying land. Bisco is a Pest Control Fungus Archer belonging to a persecuted tribe; his arrows instantly sprout colossal mushrooms wherever they land.His path collides with Milo Nekoyanagi, a gentle and brilliant young doctor running a clandestine clinic in the underground IronBase. Milo is desperately searching for a cure for his older sister, Jabi, who is slowly being consumed by the lethal Rust infection. Believing Bisco is responsible for the rust spreading, Milo confronts him, only to discover that Bisco actually possesses the true Rust-Eater. The two form an unlikely, high-stakes alliance: Bisco needs Milo’s medical expertise to navigate
the treacherous territories, while Milo needs Bisco’s fungus to save his sister and heal the world.Their quest takes a perilous turn when they are ambushed by the cruel Governor Kurokawa, who views Bisco’s people as dangerous heretics and plots to weaponize a colossal, dormant bio-weapon known as the Tetsujin—a relic of the ancient war that caused the apocalypse. Kurokawa kidnaps Jabi and imprisons Bisco, aiming to extract the secrets of the Rust-Eater for his own megalomaniacal pursuit of absolute control.Driven by fierce loyalty, Milo breaks Bisco out of captivity. Together with Milo’s fiercely protective sister Pawoo and a giant, intelligent crab named Jigi-chan, the duo mounts a daring
rescue mission and infiltrates Kurokawa’s heavily fortified fortress. A brutal, chaotic showdown ensues against Kurokawa’s private army and the awakened Tetsujin. Bisco unleashes his ultimate archery abilities, merging with the fungal spores of the wasteland, while Milo fights with unwavering medical resolve to protect his comrades.Ultimately, they defeat Kurokawa, halting his catastrophic plans to plunge Japan into further despair. With the tyrant overthrown, Jabi is rescued, and the immediate threat of the Tetsujin is neutralized. Bisco and Milo depart on another journey across the rust-choked dunes, continuing their tireless crusade to spread healing mushrooms and restore lush life to the broken world, proving that hope can bloom even in the harshest wasteland.