At birth, mages randomly acquire one of the four "crests" that represents the extent of their magical capability. Equipped with a crest specializing in creation, a man named Gaius reached the ceiling of his potential, becoming known as the world's strongest sage. Despite his overwhelming power, he is unsatisfied with his abilities and desires to possess the mark suitable for close combat. Knowing that a person's crest is unchangeable, Gaius decides to reincarnate far into the future, hoping to alter his fate. Thousands of years later, Gaius is reborn as Mathias Hildesheimer, successfully obtaining his long-coveted crest. However, he is surprised to learn that in these times, magic has vastly waned, and the techniques that were once widely used are now nothing more than just a speck of legend. Moreover, the crest that he painstakingly strived to attain is now considered the weakest—merely dubbed the "Crest of Failure." Nevertheless, Mathias naturally exceeds all expectations. He enrolls into the royal capital's Second Academy, acing every trial that comes his way. But soon after, Mathias discovers the dark truth behind humanity's downfall into magical mediocrity—demons—and endeavors to remedy the consequence of his millennia-long absence once and for all.

The OVA will tell the childhood stories of the main characters, adapting from the first volume of Satoru Yamaguchi's original light novel. Bundled with the seventh limited edition volume of the manga.

The previously bedridden Keina Kagami finds herself in the world of her favorite VRMMORPG—titled Leadale—after the life support keeping her alive fails. Reincarnated in the body of her high-level character, "Cayna," she notices that the world of Leadale is different from what she remembers playing. As she comes to learn, two hundred years have passed since she last interacted with the world. However, this does not sadden Cayna—as it means that a new journey awaits her, filled with exciting prospects and unfamiliar faces all waiting to be discovered.

Unaired episode included in the fourth Blu-ray volume. The episode will take place during the same time in episode 16 (episode 5 in second cours) and depict what Eris and Ruijerd were up to outside the main story, as teased by the comment "Goblin Extermination."