The CEO's Boss Healer

The male protagonist is just a deliveryman, but he catches the eye of a wealthy woman who offers him a marriage proposal and compensation. He refuses, only to suffer betrayal by his girlfriend later on. Returning home, he rescues a beautiful neighbor from harassment by her boss. His accidentally obtained ancient medical book reveals its powers, linking him to it, and he suddenly rises to power. Driven by revenge and a desire for a better life, the awakened protagonist seeks out the wealthy woman.