I first ran across a version of the rokurokubi when I watched the classic anime movie Vampire Hunter D on the USA Network years ago, although (as the old picture [fig.1] by the famous artist Hokusai shows) the rokurokubi are a long-standing traditional figure in the Japanese realm of Yokai (a term meaning, apparently, both a supernatural being and the realm or family to which it belongs, rather like the English terms fairy and Faerie). In Vampire Hunter D they identify themselves as "The Snake Women of Midwich," but I take this to be rather poor '80's English adaptation: they look and act at some points exactly like traditional rokurokubi, draining the life and power from D while twining their long prehensile necks around him [fig.2].
There are several different kinds of rokurokubi. One is a type of fury, cursed by their own failings to torment other transgressors against karma. Another tries to live a normal life among humans, but cannot resist showing off and scaring fools, children, drunkards, or sleepers, as they know that no-one will believe them. A third has been so successful in living life as a human that she forgets she is a rokurokubi, and only elongates her neck unconsciously while sleeping, giving anyone who is watching (like her hapless husband) a scare. This third kind may relate dreams of observing things from odd angles, unaware that this is caused by her head snaking around the room.
I next saw a group of rokurokubi while watching the "Operation Specter" part of Pom Poko, where the tanuki (supernatural raccoon dogs) are staging a parade of traditional Japanese ghost and fairy tale characters in order to inspire belief and fear among the humans who are destroying their woodland home. In one of my favorite scenes, two elderly gentlemen are drinking in an outdoor bar, opining on the foolishness of childhood beliefs, while behind them wondrous and horrific apparitions tumble by. The idea that if they would just turn away from their little lighted pool of comfort and explanations they might see that the world is full of more than they acknowledge [fig.3]. It's when I saw the three ladies behind them that I began to see there must be something behind this image.
It was further confirmed when I watched Hellboy: Sword of Storms. In this animated feature Hellboy is whisked away to a visionary, legendary Japan and encounters traditional characters, including a spider-woman, a fox-spirit, and a trio of rokurokubi [fig.4]. This third time interested me so much I finally looked into the legends and found out what was behind it all. What is still unexplained for me is why there are always three in these animated movies; I haven't seen any tale or tradition that insists on the number. Perhaps it is only because the tripling of female figures is always more threatening: three witches, three furies, three fates, all ganging up and surrounding the adventurer.