Z-Zangetsu?

THAT ISN'T ZANGETSU I keep saying that I am zangetsu. ICHIGO! what's the difference between a king and his horse? and I'm not talking about obvious stuff like one's an animal and one's person and one has two legs and one has four. form, ability and power that's what's puzzling. if their form, ability and power are exactly the same, why is it one becomes the king and leads them into battle while the other becomes the horse and carries the king? so what's the characteristic that distinguishes these two beings? there's only one answer, INSTINCT!!!