How to Use an Angel

After a wild turn of events, Yoon Kiom ends up being kidnapped by demon fanatics and is about to be sacrificed to summon a demon, whatever that is. Just when her kidnappers are about to end her life, a gorgeous man interrupts the ritual and saves all the hostages' lives. However, this was only the start of Kiom's troubles. Her rescuer, who keeps calling her "Sion," forces himself into her house and keeps lingering around. Not only that, he tells her that she's actually a demon named Gusion and that she's her prisoner. Seriously... What's up with this dude?