Everyone knows about the supernatural as they are above the lowly humans, but they have a flaw. Well, the woman do at least after all supernatural woman were cursed by powerful witches that they are unable to bare children. That is why the supernatural men seek out un expecting human woman to fix this problem they are faced. After searching became to much of a burden, to make a profit on old ways human men sell human woman to the supernatural world in the underground. Most humans don't even know of the curse anymore after so many years, but the supernatural can never forget.