An oni is a physical being, but it’s physical form is a vessel for the souls of those it has slain. It has the power to leach the soul from living beings which would add to its own life substance. As long as it get a regular supply of souls, it’s effectively immortal. They are extremely strong and resilient with large claws and fangs.
An oni can withstand most forms of physical injury (as well as regenerate). Energy, such as electricity or fire, can harm it more easily.
They have the power to become invisible. Some may have other mystic powers as well, or are even stronger or tougher then average.
Known ONI: Cratos and Bia or also known as Force and Violence.