The name is "The Demon Lord's Reincarnation: Becoming the Strongest Mage."

In a distant land, there was a powerful mage known as "The Lone Demon King." Though he was an ageless being, the villagers adored him, viewing him as their protective deity. Unfortunately, a magic organization deemed him a threat and ultimately brought about his demise. Fast forward 200 years, and he finds himself reincarnated as the second son of a noble family, now equipped with incredible magical abilities. Determined to blend in with humanity this time around, he decides to embrace his new life without seeking revenge. Despite his past as a revered guardian, he struggles with the everyday norms of human existence. As the pampered second son, he enjoys the love of his family and friends, but he’s also recognized as a formidable mage within the magic guild. However, he operates under the radar, earning the title of "Immortal Mage" while navigating the complexities of his new life. With a mix of charm and naivety, he embarks on a journey filled with magical adventures and the quest for understanding what it truly means to be human.