While only 10 years of age, Astarotte is told that she will need to begin building a harem. Because when she fully matures, her body will require a regular supply of semen to keep from wasting away, much like a vampire requires blood. Unfortunately, her mother's extreme excesses have led her to develop a fierce hatred and disgust toward all men. Astarotte demands that the first member of her harem be a human from the human world. Knowing that the Yggdrasill tree connects them to the human world, she hopes her demand would allow her to avoid the task entirely. She has a liking for Naoya.
Source from Wikipeida