The Ushi-Oni (牛鬼?, Ox Oni (demon)), or gyūki, is a creature which appears in the folklore of Japan.
There are various kinds of ushi-oni, all of them some sort of monster with a horned, bovine head.
Perhaps the most famous ushi-oni appears as a protective symbol in the Uwajima Ushi-oni Festival, which is held in late July in Uwajima of Ehime Prefecture. Something like the dragon dancers at a Chinese New Year celebration, this ushi-oni is represented with a huge, multiple-person costume with a cloth body and a carved, painted head held upon a pole. It has a sword for a tail, and is thought to drive away evil spirits.
Another well-known ushi-oni is a massive, brutal sea-monster which lives off the coast of Shimane Prefecture and other places in Western Japan and attacks fishermen. It is often depicted with a spider- or crab-like body. This ushi-oni seems to be connected to another monster called the nure-onna, who sometimes appears before an ushi-oni attack and tricks the victim into holding her child, which then becomes stuck to the person's hands and grows heavier in order to hinder escape.
Yet another ushi-oni is depicted as a statue on the grounds of the Negoroji temple in Takamatsu, Kagawa Prefecture. It is a bipedal monster with huge tusks, spurred wrists, and membranes like a flying squirrel. A sign nearby explains that this creature terrorized the area about four-hundred years ago, and was slain by a skilled archer by the name of Yamada Kurando Takakiyo (山田蔵人高清). He dedicated its horns to the temple, and they can still be seen to this day. Ushi-oni are also mentioned in Sei Shōnagon's tenth-century diary The Pillow Book, and in the Taiheiki of the fourteenth century.