Zangetsu? That isn't Zangetsu, I keep saying that I AM Zangetsu. Ichigo, what's the difference between the king and his horse? And I'm not talking about obvious stuff like one's an animal and one's a person and one has two legs and one has four. Form, ability and power, that's was puzzling if their Form, ability and power are exactly the same why is that one becomes the king and leads the horse into battle while the other becomes the horse and carries the king, so what's the characteristic at distinguishes these two beings. There's only one answer...
INSTINCT!