Soon after getting married, Wakura Mayuko's husband was murdered by the hand of a sword killer.
Losing the will to live, Mayuko had fallen into despair and tried to kill herself, but there was a young boy who pulled her heart away from the despair. His name is Kaga Isamu. Like Mayuko, his parents also lost their life to a sword killer.
Mayuko felt a connection between them, decided to adopt Isamu from orphanage and started living together.
Ten years have passed since then, Isamu have grown into a young man. While Mayuko somehow managed to regain herself
with the help from her husband's little brother Wakura Takafumi, a psychiatrist. However, the recovery also make memories with her late husband fade away slowly, and that, bring the pain to her heart.
One day, Isamu met a beautiful girl at a shrine.
Isamu is shocked by the words told by the girl.
"Mayuko will die soon"
When her heart filled with emptiness, the death shall invite her soul.
The girl claims she knows the way to save Mayuko and willing to lend her hand, but the way to rescue Mayuko, is to have the girl teach him "the way of sex".