This is one of those characters which is both creepy and tragic. The Rokurokubi (ろくろ首) is usually a woman whose neck either extends, or who becomes a disembodied head that flies around causing trouble at night. This yokai is not so malevolent, as she is just simply afflicted. There are cultural parallels to the Rokurokubi in other cultures such as The Philippines, China, and Thailand, so it is interesting to consider how this concept became a folkloric image and transmigrated around Asia.
Sometimes the Rokurokubi become this way because of horrible things that they have done, or it is a curse passed on, typically to girls, for the misdeeds of their fathers. Typically found these days in stories, and not holding much of a religious place in the minds of Japanese people, the Rokurokubi are often examples of cautionary tales in terms of what can happen to you if you break the law or the rules of conduct in society.