Again Bleach is not mine, I'm just a fan.
Underestimated
He had deemed the brash youth acceptable to appoint him as lieutenant of his own squad. He always got the proper respect from the upstart due to his station and title without exception and so allowed his crude attitude due to his upbringing in the rough streets of Rukongai to go without reprimand.
He had evaluated him as a warrior of courage, strength and unparalleled determination but he had miscalculated the motivation behind it all. Abarai had not worked so hard all these years to improve his station in life. He may have joined the academy in order to escape the poverty and filth but this drive to excel was apparently due to some misplaced idea of claiming Rukia. He had not understood until Zabimaru touched him that his number two had reached Bankai just to save his sister's life. In the privacy of his own rooms, he can allow himself a small smile at the havoc his imouto has caused in the lives of these men. The whelp will never surpass him but nonetheless, he will not underestimate him again.