Ao Oni is a lavender-skinned humanoid creature with a large distorted head that vaguely resembles a human's. It sports large, glassy black eyes; a bent nose; and a tiny, featureless body. It always has the same bemused expression on its face. The back of the One's head is black, suggesting dim lighting or hair.
The Oni also takes a more threatening appearance, as shown in Takeshi's nightmare in Version 5, should you get the best ending. In the nightmare, the Oni's eyes are more similar in appearance and is baring its teeth. With its mouth open, the player can see that the Oni has sharp teeth as well as a pair of tusks. In the nightmare the oni is somehow purple instead of lavender.