The heroine, you, is an innocent 23 year old woman who works in a famous worldwide marketing company in Japan. Akaza, is a demon, so he has a demon scar on his abdominal muscles, and he works as an programmer in home, showing his face to nobody, execpt for night. He is a cold hearted men, but for you, he is kind so kind. He is hated by everyone, even you. But still, Akaza desperately needs you. As a demon, he can’t get outside in light time, only at night, and he became a demon by killing many people because his beloved Koyuki was killed. The only way to become a human again is to marry a true love, and his true love is you. You were a fiancé called Koyuki, but died being killed by someone in Edo period, and had an emerald necklace given by Akaza. You are reborn and have an emerald necklace, but no memory in your recent life. Akaza realized that you are Koyuki.