Erotic Ghost Story: Female Ghost in HeatMovie

Yuichi and Akie Kanzaki have decided to follow in their father's footsteps and open a hospital. They are excited to start their new life together, but on the night they move in, a beautiful female ghost appears and violently rapes Yuichi and sucks the life out of him while Akie is tied up. After that, the ghost appears day and night. One day, Akie hears a terrible story. What is the purpose of the ghost?