If he had a bankai (which I reckon he would bring out through forcing out all of his spiritual pressure) it would be some sort of humungous axe-sword and it would find any kind of fear inside you and draw it out. Depending on how brave you are will depend on how quickly/slowly you will fear him, but no matter what you would eventually. E.g. After release, it would take Aizen about an hour to fear him. After release it would take Keigo a second to fear him (not that he'd have to release it anyway xD ).