Yoon Ji-Hoon, a college freshman, falls in love with his beautiful classmate Han Ah-Reum. One night, in a wave of confusion, he assumed that Ah-Reum was waiting for his confession, only to get rejected later. In desperation, he unconsciously summons the demon of greed, Mephi. Ji-Hoon signs a contract stating Mephi shall take him back to the time before he got rejected, and help him in the next 6 months to make Ah-Reum fall in love. If she still doesn't give in after the time period, Mephi will be forced to take Ji-Hoon's soul in exchange for his help.