Because the parents died early, the protagonist Takami Akitoshi has lived with the beautiful elder sister, Hitomi, alone together hiding his dirty desire toward her. One day, a mysterious girl comes into his room. Her name is Mina. Surprising, she is Death. She explains him that she came here to take his soul because he reached the end of life span. Hearing him screaming, Hitomi comes. After she knows the situation, she asks Mina to save him. Mina is moved by her earnestness, and shows them the way to extend his lifespan. If he'll have a child including a fertilized egg within a week, she will give him another 10 years life.