Following the early deaths of his parents, Takami Akitoshi has been living alone with his beautiful older sister, Hitomi, while hiding his illicit desires for her. One day, a mysterious girl named Mina enters his room. She introduces herself as Death and explains that she has come to take his soul because he has reached the end of his lifespan. Hearing his screams, Hitomi rushes in and, once the situation is explained to her, asks Mina to spare him. Moved by her sincerity, Mina tells them that if Takami fathers a child within a week, she will allow him to live for another 10 years. Upon hearing this condition, he turns his face toward Hitomi…