Physical descriptions of oni may vary, but one of the most common depictions of these monsters is that of a large, red-skinned humanoid with wild hair and fangs jutting up from the lower jaw. Sometimes they are described as possessing abnormal features like horns or additional eyes. Oni have been stated to dress themselves with loincloths made from the skin of a tiger and carry large iron clubs covered in spikes.
Oni are stated to be representatives of ill-fortune, bringers of disease and disaster that supposedly devour humans. In fact, they were originally conceived as being invisible spirits without a tangible form, only taking on their ogre-like appearance with the introduction of Buddhism to Japan and syncretizing with other mythological beings such as gaki, rakshasa and genies.