Ichigo Vs Zangetsu Final Battle Ichigo relied on zangetsu s power too much and did not rely on his own power to fight his own instinct and so ogichi tried to teach him a lesson zangetsu dissapeared during the inner hollow battle because it was necessary

Actually ichigo s reitsu level also depends on his resolve since while he has risen to the power of a captain early on in the series the times where if he has doubt he gets weaker such as when he fought against zangetsu