Ao-oni.

Ao-oni (青鬼) is the blue-skinned oni form, horned and fang-bearing like other Japanese demons but marked by a colder visual force than the red type. The blue body, iron club, and tiger pelt place it firmly inside the standard oni image, yet the color shifts the emotional register. Rather than the heat of appetite, it suggests a hard, dangerous chill, the feeling of wrath that has become fixed and merciless.

Ao-oni functions mainly in grouped demon symbolism and Setsubun-style explanations of vice. It is the oni of bad temper, grudging hostility, and anger that spills outward into harm. In that sense it interacts with humans not through one famous legend, but through annual ritual, educational posters, masks, and moral shorthand. The blue oni is the face people give to anger when they want to drive it from the house.

As with other colored oni, ao-oni belongs to a later explanatory layer added to the older oni tradition. Medieval texts knew many oni, but not necessarily this tidy moral color chart. Over time, popular Buddhist and seasonal teaching found it useful to associate specific human faults with specific demon colors, and the blue oni became the type most often linked to anger. The figure survives because the pairing is visually immediate and easy to remember.