My Cool, Devoted Husband

We agreed on a three-month contract, so how did it turn into a lifetime? And why do I have to be your wife? She's just an ordinary girl who meets him by chance and becomes the most precious person in his heart. He's aloof, domineering, cold, ruthless, and decisive in killing, a tyrant who thinks the world of himself. Yet when it comes to her, he spoils her to no end. (A devoted romance, with a clean past for both leads and a one-on-one pairing.)