Board Thread:Questions and Answers/@comment-4556003-20130502152512/@comment-44061-20130502160538

Tosen didnt like Shinigami so he didnt have a problem becoming what he became. Also it was hollowfication not becoming a hollow. the idea of hollowfication is the process as well as donning of a mask (i.e. the visoreds) that makes them hybrids at most but not actual hollows. Also Aizen didnt become a hollow or go through hollowfication at all he even states that he would never lower himself to do such a thing. His transformations are a direct result of the hogyoku. While he may look it he is no part hollow.