In the time of Minamoto no Yorimitsu, known as Raikō, strange things happened throughout the land. One of the strangest was the unexplained disappearance of many people from their own homes, in full view of friends and family. They didn’t leave the room, they didn’t fall down and die; they simply vanished, as if blotted out. No one could find out where they had gone, or how it had happened. Nor did they know how to stop it — all the land was in a great panic.
Yorimitsu called his advisors and diviners to investigate. They learned that in the days of the Emperor Saga Tennō, (about one hundred and fifty years earlier), there was a lady of the court, the daughter of a high official, who feared that she was losing her lover to another woman. This lady became so jealous that she secluded herself in the shrine of Kibune for seven days, and prayed to the kami of the shrine:
“Grant that I may be changed into an oni (demon), so that I can kill the woman who is stealing my lover.”
The kami pitied the woman, and granted her wish.
“If you wish to become an oni, you must change your appearance and bathe in the Uji River for three times seven days.”
Overjoyed, the lady returned home and hid herself away. The divided her long hair into five tresses, which she shaped into five horns. She reddened her face and body with vermilion, and on her head she placed a tripod with a torch attached to each leg. In her mouth she held another torch, flaming at both ends. In this attire she rushed south down the Yamato highway after dark. The poor people who saw her thought for sure that she was a demon — some of them were so terrified that they died from their fear.

Image: Wikipedia
The lady reached the Uji river and bathed there for three times seven days, and as the kami had promised, transformed living into an oni. She became known as Uji-no-Hashihime, or the Lady of Uji Bridge. As an oni, she killed not only her rival, but her lover as well, along with all of their relatives, rich and poor. When she wanted to kill a man, she would show herself as a woman, and when her intended victim was a woman, she would show herself as a man. All the people of the city were so terrified that they would shut themselves in their homes after the Hour of the Monkey (4 pm), neither going out nor allowing anyone in.