Setsuna Kashiwagi's only desire is for his sister to live a happy life. Weak, frail, and constantly bullied, Setsuna believes he is nothing but a burden to his sister and decides to take his own life. As he prepares to jump off a bridge, a mysterious man appears and presents him with an unusual offer. He offers 10 million yen in exchange for Setsuna's life. If he accepts the contract, after one year, Setsuna will end his life in a manner the man chooses. Skeptical at first, Setsuna accepts. The next morning, thinking it was all just a dream, Setsuna awakens to find two beautiful women sitting beside him. They are Kanna and Rena, Oni princesses who have come to protect Setsuna. The catch: one of them will consume his heart in one year.
