Tetsuzaemon is Sajin's lieutenant.
When he first fought Tosen, the two were convinced that there was no other way to support their beliefs except kill each other, until Ben, using Ultimate Echo Echo, was able to knock out his friend. He then decided not to kill his friend, believing that there was a chance his old friend could be redeemed. When Ben convinced Tosen that following Aizen was a mistake, Sajin promised the redeemed Shinigami that the murderer of Tosen's beloved friend would be facing charges.
Sajin is grateful to Ben for not only defeating Aizen and ending the war, but for redeeming his long time friend Tosen.