He's 6,000 years old, and he's 6'5 "in Oni form, but 8'3" in his full demon form. He has canine like teeth and nails like claws and horns. 

His full demon form is an 8'3 " tall, all black entity that only has 2 white milky eyes and a lion like mane along his neck and back, and hundreds of nail like teeth that protrude from his mouth into a creepy smile.

In his Oni form, he looks human but has nails, horns, and wolf like teeth, and is 6'5 "height. 