Originating in the Sarlonan province of Borunan, Oni are a subspecies of Borunan Ogre. The Inspired teach the Oni that they are living prisons for fiends, that their ancestors bound these evil sprits to their bloodlines (in much the same way that the Kalashtar bound themselves to human bloodlines) to prevent them from reforming and continuing to wreak havoc.
Oni are large, humanoid creatures with a huge variety in physical appearance. if the story they are taught is true, it is possible that this is due to the Oni taking on physical characteristics of the fiends that supposedly reside within them. They are also all innately magical, all of them can fly and become invisible, and many of them are capable of other magic without any training whatsoever.
The Oni of Sarlona are taught that they must live their lives in devotion and service to the Inspired, or they risk losing control of themselves to the fiend that is imprisoned within their flesh. Not all of them accept this, and there was a notable migration of Oni to Khorvaire in the last few decades. Primarily, these Oni are concentrated in Droaam, where they serve as specialists and agents of the Daughters of Sora Kell.