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.

Orichalcum is a mystical metal material that gives great powers to the life form that possesses it. Many Eons ago, the Orichalcum was split into three and landed on Earth. The metal then took the form of three relics: Skanda’s Vajra, Jew’s Cross, and the Sword of Alexander. Anyone able to re-unite these three Orichalcum relics would then obtain the powers of a God. Now two rival aliens are in a heated race to reunite the Orichalcum. They land in Edo era Tokyo where the relics are thought to exist.