Tennomifune Academy is an elite institution for the best and the brightest, with the exception of Class 1-7, the so-called Happiness Class. Each member of the classroom copes with personal misfortunes, and the special class is geared to help them move past their issues and find true happiness. After being accepted into the academy, An Hanakoizumi, Ruri Hibarigaoka, and Botan Kumegawa find themselves placed into the Happiness Class, plagued by dreadful luck, love problems, and bad health respectively. Alongside their classmates, they do their best to overcome the difficulties they are faced with in pursuit of a life filled with joy.

Ritsuka Tachibana has always been a good student, so she is completely shocked when she is suddenly summoned by the student council for breaking school rules. Led by Rem Kaginuki, the student council—also consisting of Urie Sogami, Shiki Natsumezaka, and Mage Nanashiro—tries to interrogate her, but it soon becomes clear that they have ulterior motives. However, this is only the beginning of Ritsuka's misfortune. When her mother gets kidnapped, her life is turned upside down, and Ritsuka gets drawn into a battle for supremacy between vampires and devils. Both groups are searching for the Grimoire, a forbidden item that allows its owner to rule the world, and Ritsuka is somehow connected to this strange artifact. The return of Ritsuka's protective brother Lindo from overseas gives her hope that life could return to normal. But even her sibling is harboring his own dark secrets. Ritsuka begins to question whom she can trust, and if she can ignore her growing attraction toward the devilishly handsome student council members.

Ichirou Suzuki, a programmer nearing his thirties, is drowning in work. Worn out, he eventually has a chance to catch up on sleep, only to wake up and discover himself in a fantasy RPG world, which is mashed together from the games he was debugging in reality. In this new place, he realizes that not only has his appearance changed to a younger version of himself, but his name has also changed to Satou, a nickname he used while running beta tests on games. However, before Satou can fully grasp his situation, an army of lizardmen launch an assault on him. Forced to cast a powerful spell in retaliation, Satou wipes them out completely and his level is boosted to 310, effectively maximizing his stats. Now, as a high-leveled adventurer armed with a plethora of skills and no way to return to reality, Satou sets out to explore this magical new world.

Some time ago, the influential and powerful Toue Inc. bought the island of Midorijima, Japan, with the plans of building Platinum Jail—a luxurious utopian facility. Those who are lucky enough to call it home are the wealthiest citizens in the world. The original residents of the island, however, were forced to relocate to the Old Residential District; and after the completion of Platinum Jail, they were completely abandoned. Rib and Rhyme are the most common games played on the island. Rib is an old school game in which gangs engage in turf wars against each other, while Rhyme is a technologically advanced game wherein participants fight in a virtual reality. To be able to play Rhyme, you must have an All-Mate (an AI that typically looks like a pet), and the match must be mediated by an Usui. Aoba Seragaki has no interest in playing either game; he prefers to live a peaceful life with his grandmother and All-Mate, Ren. However, after getting forcefully dragged into a dangerous Rhyme match and hearing rumors about disappearing Rib players, all of Aoba's hopes of living a normal life are completely abolished.