Suggested by iKnowledge Kazuya has a demon form that makes him a true threat, He has solid range and a whole lot of attack power. Still, that will not be enough to take Ren down. Ren is from the prestigious Tao family and has a lot of high level modes of attack. His sheer volume of energy is massive by the end of Shaman King. When you factor in his speed as well then he will be able to overwhelm Kazuya with massive attacks of pure power. Ren wins.