According to Japanese beliefs, a kuro bōzu is a dark, shadowy yōkai which looks somewhat like a bald-headed Buddhist monk — however, its exact appearance is vague and difficult to make out. It’s entire body is black, and it wears black robes. Its face has somewhat bestial features. It has a long tongue, and it reeks of rotting fish. Its hands and feet are said to be indiscernible. It can change its height rapidly, becoming a towering monster in an instant. It is extremely fast, and can run as fast as if it were flying.

Kuro bōzu haunt areas inhabited by humans. They come out at night, sneaking into houses after everyone is asleep. They creep up to their victims — primarily women — and suck the breath out of their mouths. They also slide their putrid tongues into the mouths, ears, and all over the faces of their victims. Those visited repeatedly by kuro bōzu become very ill.

Kuro bōzu didn’t appear in folklore until the Meiji period, so they are relatively new by yōkai standards. Because of the wide variations in reports, it is hard to come up with a clear picture of this yōkai’s identity. Some experts believe they are a kind of nopperabō, due to their vague and indiscernible features. Some compare them to yamachichi, who also sneak into houses to steal the breath of sleeping humans. Its size-changing abilities and monk-like appearance suggest that it may be a variety of taka nyūdō. Still others say that it is one of the forms taken by magical kawauso.

The most well known kuro bōzu report comes from the early Meiji period, from a newspaper article in the Hōchi Shinbun:

The encounter took place at a certain carpenter’s house in Kanda, Tokyo. At midnight, a black, shadowy figure shaped like a monk suddenly appeared in the house. The creature entered the bedroom where husband and wife were sleeping. It climbed over the carpenter’s sleeping wife and stuck its tongue in her ears and mouth. Then it licked her all over. The creature smelled like foul garbage. The smell was so noxious that the family became ill.

Again and again for several nights, the kuro bōzu returned to assault the carpenter’s wife. Finally, she could not put up with it anymore. She left her husband and went to stay with some relatives. According to the carpenter, after his wife left, the black monk stopped coming.