The oni, or two-horned devil, is a popular image in the Japanese tattoo artwork of today. They are probably the most common of the ghostly beings in Japanese cosmology and are typically depicted as rampaging, violent, and cruel. Almost always shown with horns, their faces can be quite varied, similar to noh masks, and are typically pink, red, or blue-grey.
In general, the oni is a fearsome supernatural creature. They have been described variously as guardians of Buddhist hell, demons who act as torturers there, pranksters, devourers of human victims, hunters of sinners, and bringers of disease and epidemics.
There is also a tradition, however, in older tales, that they can apparently be converted to Buddhism and become benevolent protectors – such as monks who become an oni after death in order to protect a temple.
