Henkyougurashi no Maou, Tensei shite Saikyou no Majutsushi ni Naru

For generations, an ageless mage known as the Lone Demon King lived quietly on the frontier, serving as a beloved guardian deity to the local villagers. Despite his deep affection for humanity, his mere existence was deemed a threat by a powerful magical organization, which ultimately orchestrated his destruction. Two centuries later, he is reborn as the second son of a noble family, awakening in a new life armed with unparalleled magical power. Having always cherished humans, he harbors no desire for revenge against those who killed him. Instead, he resolves to spend this new life doing what he has always secretly wanted: pretending to be human. However, blending into society proves far more difficult than mastering magic. Accustomed to his former roles as a solitary regional protector and now a sheltered aristocrat, he remains entirely oblivious to everyday common sense and has no idea how to simply relax. Though he is deeply loved by his new family and friends, his extraordinary abilities inevitably draw attention. While the magical guild reveres him as an unmatched prodigy, he operates from the shadows, unknowingly cementing his legend as the Immortal Mage.