The Ao Oni is the enigmatic primary antagonist of Ao Oni. It is a creature that lives in the abandoned mansion on the outskirts of town. Not much is known about the Oni but it comes from a world with many creatures that resemble it. It is known to feed upon people and shapeshift. Specifically in versions 6.22 and 6.23, it has been shown that after the Oni kills, the victim becomes an Oni themself, turning against the main protagonist, in this case, Hiroshi. These transformed Onis also seem to be able to take the form of the original character. This is shown when "Takuro" asked Hiroshi if he could go with him, when Hiroshi goes to put the blue piece on the paper, Takuro turns into a Character Oni and chases Hiroshi.
The Oni is a lavender-skinned humanoid creature with a large distorted head that vaguely resembles a human. He sports large, glassy eyes, a bent nose, and a tiny, featureless body. He always has the same bemused expression on his face.
In version 5.2, the Oni takes a more threatening appearance in Takeshi's nightmare, should you get the best ending. In the nightmare, the Oni's eyes are more similar in appearance and is bearing it's teeth. With it's mouth open, the player can see that the Oni has sharp teeth as well as tusks.
Ao is a Japanese word meaning "blue" and Oni meaning "demon" so its name literally translates to "Blue Demon".
- Although Ao Oni means "Blue Ogre", many people refer to it as "Blue Demon" or "Blue Troll".
- In-game, even though it is named "The Blue Ogre/Demon", it's coloring is actually closer to a lavender hue. It is unknown whether it was a sprite error or intentional. It is possible that "Ao / Blue" could simply be a proper name, and not a description of his actual color.
- According to the ending of the game, the Oni sees through a form of thermal-based vision, similar to the titular alien from the movie "Predator".