>>23092637Contextually, its usually a girl . Within Japanese Folklore there are a few different stories about Futakuchi-onna (women with two mouths) and other ghosts that have a mouth they prefer (or are forced) to use hidden on the back of their head and prehensile hair that they use to feed it.
The first version of the story I read(probably the wikipedia version) is about a skinflint old man who didn't want to pay to feed his wife, so he didn't get married until he found a woman who ate nothing while in his presence. They get married and his stores of rice start disappearing, and eventually he notices calls her out and gets devoured himself.
The second version of the story has a mother who is incredibly stingy and doesn't feed her kids at all while she eats as much as she wants. Eventually, a youkai starts haunting her (unlike the other story, where wife is the the monster) and opens its mouth on the back of her head while taking control of her hair. Every time the mother tries to eat, the mouther takes the food from her lips and consumes it instead. The kids get to eat and grow stronger, the mother dies, and the monster finds a new deserving host body.