"Seiichi Hiiragi is an ugly, revolting, dirty, smelly fatass"—these are the insults hurled at him one after another about his appearance. Such was Seiichi's miserable school life. One day, a voice claiming to be a God announced over the public address system to prepare to be transported to another world. The entire school, including Seiichi, were sent to a fantasy world featuring game-like elements such as levels, stats, and skills. However, the God still had preparations to complete for the transfer, and would send them over as soon as the hero summoning ritual was ready. The classes all formed groups to wait for the transfer, but Seiichi alone was excluded, and as such was summoned to a different area. After being transported, the first thing Seiichi ate was the "Fruit of Evolution," which would come to greatly change his life... This story follows Seiichi from being bullied by his classmates, neglected as a companion, to his hard work, positive attitude, and surviving in this new world. As a result, he becomes one of the champions before he knows it.

In Tokyo's downtown district of Ikebukuro, amidst many strange rumors and warnings of anonymous gangs and dangerous occupants, one urban legend stands out above the rest—the existence of a headless "Black Rider" who is said to be seen driving a jet-black motorcycle through the city streets. Mikado Ryuugamine has always longed for the excitement of the city life, and an invitation from a childhood friend convinces him to move to Tokyo. Witnessing the Black Rider on his first day in the city, his wishes already seem to have been granted. But as supernatural events begin to occur, ordinary citizens like himself, along with Ikebukuro's most colorful inhabitants, are mixed up in the commotion breaking out in their city.

In a world of magic, the powers and future of a mage are predetermined at birth through so-called "Marks"—four symbols that categorize a human's aptitude for magic. Lamenting the fact that his mark was considered ill-suited for combat and only useful for magic augmentation, an incredibly skilled sage decided to reincarnate thousands years in the future. Reborn as Mathias Hildesheimr—a six-year-old boy and the third son of a duke's family—he attains the mark of close combat he always desired. Unfortunately, it is also discovered that mankind's knowledge of magic and swordsmanship has drastically deteriorated in this era; only shoddy magic equipment can be sporadically found, while even the most basic spells have been forgotten. To add insult to injury, his current mark, once hailed as the most powerful, is now viewed as the worst. When Mathias becomes 12 years old, his unrivaled swordsmanship lands him in the Second Royal Academy. Shattering prejudices, he promptly makes ripples in the academy and beyond. However, the former sage uncovers signs of dark forces working in the shadows, and with humanity weaker than ever, it is up to Mathias to thwart their evil plans. [Written by MAL Rewrite]

Following their heroic efforts at Walter Park, the students of the misfit class return to Babyls Demon School after their summer vacation. What awaits them is not only adoration and admiration but also the shocking revelation that, in order to stay in the luxurious Royal One classroom, the entire class must be promoted to Dalet rank before entering the second year. As the Harvest and Music Festivals are right around the corner, there seem to be ample opportunities to rank up. Doing so will not be simple, however, as no class thus far has managed to accomplish such a feat. Hoping to give the misfit class a chance to achieve the improbable, the school appoints special tutors to aid in confronting the challenges that lie ahead. With his sights set beyond Dalet, Iruma Suzuki decides to take strides toward the goal of ranking up, starting with gaining acknowledgement from his special tutor: the short-tempered and selfish Bachiko Barbatos.