Takuya Arima is a young student whose father, a historian who has conducted various researches, disappeared recently. During a summer vacation Takuya receives a peculiar package from his missing father, along with a letter containing information about the existence of various parallel worlds. At first Takuya doesn't take it seriously, but soon he realizes that he possesses a device that allows him to travel to alternate dimensions. Is his father alive, after all? If so, where is he? (Source: VNDB)

One day, class 3-E of Kunugigaoka Magic School receives a special mission: to kill their homeroom teacher, the Demon King Koro-sensei. To increase their chances of succeeding, the class searches for the three most powerful warriors—Karma Akabane, Itona Horibe, and Ritsu—who later join their company. Even with their help, accomplishing the mission becomes an insurmountable task as they are not the only ones after the Demon King's life. Koro-sensei Quest! tells the comedic adventures of Nagisa Shiota and class 3-E as chibi magical students. Trained by none other than their very target, the students encounter challenging, yet hilarious situations all through the perilous mission of defeating the Demon King.

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 Ford Darkness Dustiness 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.