Do Do Hee is the successor of the Future Group. She has an arrogant and cool-headed personality, who doesn’t trust in anyone. She is cynical about love. Do Do Hee gets involved with a demon named Jung Koo Won and makes a contract marriage with him. She faces big changes in her life. Jung Koo Won is a demon. He can live for eternity by making dangerous, but sweet deals with humans who endure hellish lives. He looks down upon humans and he has prowled over this world like an apex predator for 200 years. He gets involved with Do Do Hee and somehow loses his power all of a sudden. He then enters into a contract marriage with her. To prevent his own extinction, he must protect Do Do Hee who has taken all of his power. Their relationship develops romantically.