Spiral Over / In a Spiral

Mizuro and Nazumi are two twin sisters who are completely unlike each other. One night, after they walked their friend Tomo home, the girls heard a terrible female scream from somewhere in the park. The next day, Tomo confessed to Mizuro-chan that it was her scream, and she was raped right in the park. Later, she begins to behave strangely and constantly sexually harasses Mizuro. After some time, Tomo dies without any particular reason, and Mizuro and Nazumi's father is tasked with investigating the girl's sudden death. Mizuro herself decides to investigate the murder of her beloved friend and learns not only the cause of Tomo's death, but also that Nazumi is not really her sister, but just an ordinary clone...