A brief description of the manga The Demon King of the Frontier Life, Reincarnated to Become the Strongest MageT:
A magician named “King of Lonely Demons” lived at the border.
He was just a creature that never got old, but the villagers loved him as a kind of guardian deity.
However, he was destroyed by a magical organization that considered his existence dangerous.
After 200 years, he was transformed into the second son of an aristocrat and gained enormous magical power.
However, he loved mankind, and not particularly thinking about revenge, he decided, in this life, to pretend to be human.
In his past life, he was a deity guardian of the region, and in this life he is a local aristocrat, but he does not know common sense. He does not know how to treat everything calmly.
As the second son of an aristocrat, he was loved by his family and friends, and although he was considered a master of magic in the magic guild, he becomes an “immortal magician” behind the scenes.