Matthias Hildesheimer was once Gaius, an immensely powerful sage over 5000 years prior, limited by his First Crest's unsuitability for combat despite its magic augmentation. Seeking greater power, especially physical combat prowess, he used reincarnation magic to be reborn in a distant future.

He emerged as Matthias, the third son of a duke, now possessing the coveted Fourth Crest optimized for close combat. This ideal crest, however, faced prejudice in his new era, mistakenly viewed as the weakest. He discovered humanity's magical knowledge and swordsmanship had severely deteriorated; basic spells were forgotten and only inferior magical equipment remained.

Enrolling in the Second Royal Academy at twelve due to unmatched swordsmanship, Matthias challenged prevailing crest biases. He formed key bonds: with Lurie Abendroth, bearer of the First Crest he once had who developed feelings for him; with Alma Lepucius, skilled in archery despite her Second Crest's magical limitations; and with Iris, an ancient black dragon who recognized his true identity as Gaius but kept it secret, accompanying him at the academy in human form.

Matthias's core mission involved investigating signs of demonic influence behind humanity's decline and preparing to confront powerful extra-dimensional monsters threatening existence. His actions focused on restoring lost magical knowledge, enhancing allies' capabilities, and thwarting emerging dark forces.