Oni appears as a lithe, muscular Void Tiefling Standing 6 feet tall. His skin shines like polished obsidian, and his eyes, hair and runes (that snake his body) glow a ultra violet hue. The horns atop his head are of incredible hardness, able to notch even adamantite. Oni was born in the infinate layers of the Abyss, a region of intense, extreme, and unforgiving climates, with layers consisting of overwhelmingly fierce desert sandstorms; explosively unstable volcanic activity, boiling lava, and molten rock; blinding, sub-zero Arctic glaciers; bottomless oceans filled with enormous leviathans; nauseatingly putrid environments saturated with disease-causing fungi; and the endless, existential void of infinite space. Oni is from the dark and formless void, where unimaginable horrors reside.
Oni infiltrated the surface to devour the land's most promising creatures. With each kill he absorbs his prey's strength, evolving and honing his fighting style to grow more powerful. Oni hungers most to conquer and consume  Kuma, the one being he considers his equal.
When Oni crossed over into this world, he was ravenous. The animals he first encountered were too small to fuel the rapid evolution he craved. Oni focused his hunger on the most dangerous creatures he could find, risking his life to satisfy his need. With each kill he feasted and changed, becoming a stronger, faster predator. Oni soon chased his prey with unrestrained aggression, believing he was unstoppable. One day, while savoring a fresh kill, the predator became the prey. From cover a creature pounced in a blur of fangs and steel, tackling him to the ground. It roared in his face slashing and clawing, and Oni felt his blood spill for the first time. Yelling in fury, he gave a flurry of blows at the brute's eyes driving it back. They fought from sunset to sunrise. Finally, near death, they reluctantly separated. As his wounds closed, Oni burned with anticipation at the idea of devouring one who could match the Void's strength. He resumed his search for powerful prey with renewed vigor. Someday, Oni will feast on Kuma..