A plague-like wind blows across the arid, sandy expanse of a post-apocalyptic Japan. As it sweeps over the living and nonliving alike, rust is all that remains in its wake. The cause of the catastrophic state of the world is believed to be mushroom spores. Bisco Akaboshi, known as the "Man-Eating Mushroom," is a wanted criminal archer whose arrows instantly grow mushrooms wherever they land. However, he is in truth a "Mushroom Protector," a person who spreads fungi in order to enrich the land and return it to its previous state. Alongside the crab Akutagawa and young doctor Milo Nekoyanagi, Bisco ventures through the wastelands of Japan searching for the legendary "Sabikui"—a panacean mushroom said to devour all forms of rust.

A millennium has passed since the catastrophic nuclear war named the "Seven Days of Fire," which destroyed nearly all life on Earth. Humanity now lives in a constant struggle against the treacherous jungle that has evolved in response to the destruction caused by mankind. Filled with poisonous spores and enormous insects, the jungle spreads rapidly across the Earth and threatens to swallow the remnants of the human race.

Away from the jungle exists a peaceful farming kingdom known as the "Valley of the Wind," whose placement by the sea frees it from the spread of the jungle's deadly toxins. The Valley's charismatic young princess, Nausicaä, finds her tranquil kingdom disturbed when an airship from the kingdom of Tolmekia crashes violently in the Valley. After Nausicaä and the citizens of the Valley find a sinister pulsating object in the wreckage, the Valley is suddenly invaded by the Tolmekian military, who intend to revive a dangerous weapon from the Seven Days of Fire. Now Nausicaä must fight to stop the Tolmekians from plunging the Earth into a cataclysm which humanity could never survive, while also protecting the Valley from the encroaching forces of the toxic jungle.

[Written by MAL Rewrite]

While exploring Wiz's magic shop with his party, Kazuma Satou finds a magical wish-granting choker and decides to try it on. Only then does Wiz tell him that the choker strangles its wearer to death in four days unless their desires are fulfilled. This wouldn't be a problem if Kazuma knew what his wish was. Fearing for Kazuma's life, Aqua, Megumin, and Lalatina "Darkness" Dustiness Ford all agree to do his bidding in order to satisfy his desires and hopefully grant his wish, no matter what he asks for...

It is not strange that the Demon Lord's forces fear the Crimson Demons, the clan from which Megumin and Yunyun originate. Even if the Demon Lord's generals attack their village, the Crimson Demons can just easily brush them off with their supreme mastery of advanced and overpowered magic.

When Yunyun receives a seemingly serious letter regarding a potential disaster coming to her hometown, she immediately informs Kazuma Satou and the rest of his party. After a series of wacky misunderstandings, it turns out to be a mere prank by her fellow demon who wants to be an author. Even so, Megumin becomes worried about her family and sets out toward the Crimson Demons' village with the gang.

There, Kazuma and the others decide to sightsee the wonders of Megumin's birthplace. However, they soon come to realize that the nonsense threat they received might have been more than just a joke.