The Element Encyclopedia of Witchcraft: The Complete A-Z for the Entire Magical World - Judika Illes 2005
The Horned One and The Devil
Horned spirits were demonized in places other than Europe. Often described as “Japanese demons,” Oni are a class of Japanese spirits. They are shaggy, horned, and tusked with vivid red, blue or black skin.
“Oni” is also frequently translated into English as “devil” or “ogre.” However unlike the European ogre, Oni are not stupid or slow but very smart and thus formidable opponents. Allegedly if an Oni loses a limb, it reconnects and heals instantly. They are now typically portrayed as vicious, malevolent, ominous demons up to no good.
Oni carry and wield the kanabo, a large spiked iron bar. The feared subject of horror stories, allegedly some Oni enjoy the taste of human flesh. This legend of the human-eating oni may derive from their origins as spirits of death. At least as far back as the second-century CE, Oni, then both male and female, served as supervisors in the Realm of Death. Although spirits of death are rarely popular, the Oni was perceived as fulfilling a spiritual function. Although dangerous, they were not evil and sometimes served as guardian spirits.
The Kamakura Period (c.1185—1333 CE) saw the rise of the new Samurai class and the concurrent demonization of Oni. The Oni evolved into enemies of the Samurai. A frequent subject of legends involves Samurai foiling evil Oni. Oni became increasingly masculine and malevolent. True female Oni became rare; the Hannya, a horned female spirit, became perceived as the Oni’s female counterpart.
Oni and Hannya have something of the same nature; both are spiritual entities—some Hannya and Oni have always been spiritual entities but others are transformed humans, sort of vengeful angry ghosts possessing the extraordinary powers of demons.
Men who die in states of excess anger may be transformed into Oni after death
Women who die in states of excess rage or jealousy may be transformed into Hannya
Although Oni are now almost exclusively male spirits, their affiliation is with human women. When male Oni wish to travel incognito or disguise their true identity, they transform into the image of human women. The implication is that any woman might be an Oni in disguise.
Demonized in popular entertainment, among esoteric scholars Oni remain spirits of anger and justice; like Shiva they both destroy and protect. Oni guard the gates of the various Buddhist hells and Realms of Death.
See also Hannya, Shiva.