I just finished watching Bleach. I wonder what was it about Matsumoto Rangiku that Ichimaru Gin wanted to avenge/protect? Also, what would he have been thinking after he successfully extracted the Hogyoku from Aizen's body?
Gin found a collapsed Rangiku. They began living together in Rukongai. One night Gin spotted Aizen and three other Shinigami in a forest. He watches Aizen receive a pink ball of energy from one of the Shinigami. Gin had witnessed these three Shinigami leaving the area where he found Rangiku. It's implied that they stole the pink spiritual energy from her. For this reason, Gin vows to get revenge on Aizen.
As for what he was thinking after extracting the Hogyoku, I can only assume that he believed he was successful in killing Aizen and avenging Rangiku.