Too strong a wizard is reincarnated after a thousand years of boredom with the life around him. But what the man who was reincarnated as Kurt saw was a world in which magical civilization declined and wizards much weaker than a thousand years ago. So Kurt was mistakenly perceived as' flawed magic ', but only he knows.
"Defective magic? Say what? Isn't it the strongest/best golden color"
Eventually the strongest demon mentor goes to the School of Magic and will be unrivalled in his second life!