Warning: Spoilers ahead.
The anime begins with what looks like Tokyo being hit by an atomic bomb. Classic set-up.
Time skips far to the future. Tokyo is rusty and covered in sand like a desert. A traveling monk is trying to pass through a gate checkpoint into Imihama supposedly on a pilgrimage but we can’t see his face because it’s bandaged. He talks to the gate guards who inform him of a highly wanted man pictured in a poster, named Akaboshi Bisco. You can probably guess, the bandaged man is this dude. Anyways, he’s wanted for covering a whole mountain in mushrooms, and we learn that’s a really bad thing in this world.
The scene cuts to part of Imihama that looks cyberpunk. A really trashy, ghetto. A madam of a whore house starts telling a story to her whores about Tetsujin, and a Mushroom Keeper. Not really important to know now. Then we meet the series’ other main character, Doctor Milo Nekoyanagi. A skilled, kind doctor who treats the poor of the city without requiring payment. He’s also a bishounen. Anyways, he’s good at helping treat people with the Rusting disease. That turns their body… rusty.
After work, Nekoyanagi stops by a food vendor for food, and to acquire illegal mushrooms. He gets back home to his sister Pawoo, who is suffering from Rusting. He secretly uses the illegal mushrooms in research to try to create a cure for Rusting. He hasn’t been having much luck.
While working, Pawoo notices on the news that a mushroom terrorist attack is happening not too far away, commited by Bisco. So Pawoo tells Milo to be careful when he goes out.
After another boring gate checkpoint scene, it cuts to a scene with some mysterious girl in a bunny mask trying to… kill giant grabs with a missile I think. But the missile is stopped by an arrow… that produces mushrooms that cause the missile to blow up. Okay.
Milo goes out to trade with the food vendor again. A random boy steals his bag and runs away with it. Milo is able to catch up and treat the boy’s scorpion sting in an alley. But the evil scumbag Governor Kurokawa introduces himself at this moment too. He obviously looks down on the people of his city, but values a genius like Milo.
Their talk is cut short when Bisco starts shooting up the city with building-sized mushrooms. The governor’s bunny people try to stop him, but they suck. Bisco makes eye contact with Milo for a second, before he ejects himself with a giant mushroom. Escaping the bunnies.
Milo gets home and sees Pawoo suit up in her gear. As a member of the police or something, she feels it’s her duty to stop this terrorist. Even though she’s sick. She knocks out Milo who protests her leaving.
A pink haired girl named Chiroru, one of the bunny people is thrown in front of Kurokawa. She probably shot the missile earlier.
Milo wakes up excited to research the new unique mushrooms. Bisco appears behind him!