Setsuna Kashiwagi is weak, bullied, and pessimistic about life. As he stands on the verge of jumping off a bridge, a mysterious man appears behind him and offers a contract: "10 million yen in exchange for your life in a year." Initially skeptical, Setsuna accepts. The next morning, waking up and assuming it was all a dream, he notices two beautiful women sitting beside him. They are Kanna and Rena Kurohime, demon princesses who have come to claim his heart in a year.