According to Japanese belief, Yamauba are the old hags and witches of the Japanese mountains and forests. A kind of kijo, yama uba were once human, but were corrupted and transformed into monsters. They usually appear as kind old ladies. Some sport horns or fangs, but most often they look just like ordinary elderly women, with no sign of their evil nature until they attack.

Yamauba live alone in huts by the road, occasionally offering shelter, food, and a place to sleep for the night to weary travelers. Late at night when their guests are fast asleep, they transform into their true shape — an ugly, old, demonic witch — and try to catch and eat their guests, often using powerful magic. Stories of encounters with yamauba have been passed along and spread by those few travelers lucky enough to escape with their lives, and are frequently told as bedtime stories to disobedient children.

Sometimes yamauba are created when young women accused of crimes or wicked deeds flee into the wilderness and live out their lives in exile, transforming gradually over many years as they grow older. In some cases, though, their origin can be explained by an old custom from times of famine or economic hardship. When it became impossible to feed everyone in the family, often times families had to make a hard choice: remove one family member so that the rest can survive. Often this was the newly born or the elderly. Some families led their senile mothers deep into the woods and left them there to die. These abandoned old women, either out of rage or desperation, transformed into horrible monsters who feed on humans and practice black magic.