Saikyou Onmyouji no Isekai Tenseiki

Haruyoshi Kuga reached the height of exorcist arts, only for his overwhelming power to make him a target of envy and betrayal. With his final breath, he uses a reincarnation spell and vows that his next life will be guided by cunning rather than strength alone. He awakens as Seika Lamprogue, the illegitimate son of a noble family in a world where magical ability determines a person's worth. By its standards, Seika appears to have almost none.

What his new family cannot see is that the techniques, spirits, and knowledge from his previous life do not follow this world's magical rules. Seika tries to conceal the true extent of his abilities while forming alliances that might keep him from repeating his old fate. Yet the more he hides, the more extraordinary circumstances seem to gather around him.