In the folklore of Japan, the ushi-oni (牛鬼,lit. "ox ogre"), or gyūki, is the name of several different creatures having in common a horned, bovine head.
The most famous is a sea monster with a horned head like a bull or an oni, and a body like a gigantic crab or spider which is said to lurk in the southern Sea of Japan, from Shimane prefecture down through Northern Kyuushuu, and devour anyone unlucky enough to be caught on the beach.
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.
Another famous ushi-oni appears as a protective symbol in the Ushi-oni-matsuri, 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.
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.
Other ushi-oni like the freshwater gyuki of Shikoku or the bizarre ushi-oni that terrorized Negoro also appear in famous old literature such as the Sei Shonagon's tenth-century diary The Pillow Book, and in the Taiheiki of the fourteenth century.
- In the Yu-Gi-Oh! trading card game there are two cards featuring ushi-oni - "Ushi Oni" is a bull fiend with four octopus tentacles on its back, and "Abare Ushioni" is a bull monster.
- In the anime Karas, a bloodthirsty Ushi-Oni becomes a mechanized 'Mikura' concealing itself in the form of a police chief.
- In the TV sentai series Ninja Sentai Kakuranger - One of the Youkai Gundan is an ushi-oni.
- In Gegege no Kitarou (Gameboy Advance) - Ushi-oni appears in this game as a boss, menacing a seaside town.