Disclaimer: Bleach is not mine, by extension, neither are any of the characters.
Ichimaru Gin
His vision was fading slowly. He was dying and he knew it, but he had no regrets save he wished he had had more time to spend with Rangiku. It was all for her; he lived and died for her because she was the only one who saw behind his shady exterior and actually tried to get to know him – she had a pure heart and he had to protect that heart, even if it cost him his life.
The traitor was speaking, something about fear and sacrifice. What a joke, Aizen did not know true fear; he had not seen everything he had worked for almost crumble before his very eyes, like when he saw Rangiku and feared she would drop dead any minute due to her injuries, at least not yet. When his plan revealed itself, then Aizen would know true fear. If he truly believed that Gin's plan was only one level deep then he clearly did not understand just what kind of person he, Gin, was. He had no idea what kind of deceiver he was dealing with.
The pain that spread through him as his arm was ripped off was tolerable because it meant Aizen felt he had won. What he did not know was that even if Kurosaki failed to arrive, he had lost; he had lost the moment Gin's sword pierced his skin. He had promised Aizen that he, Aizen, would die with a hole in his heart, although Gin talked lightly he never made a promise he did not plan on keeping.
Aizen's sword ripped through him and that's when he knew he was dead, but it was all right because Rangiku would be fine and she would never have to live under the rule of such a mad-man. She would live the happy, care-free life she had lived in Seretei before he, Tousen and Aizen defected. She would never have to suffer again or cry again. Maybe he would not be there to make sure of it, but he trusted his lieutenant – sorry, former lieutenant – would fulfill his last orders. He trusted Kira would at have enough respect for their 'friendship', despite how much he tormented the poor soul, to look after her in his absence.
His time had come; he was slipping away and he knew it. She would never know that he died so he could infect the hougyoku with his zanpaktou's poison, so it would tear Aizen apart from the inside out and he would never get to lay a hand on her. She would never know about his sacrifice and he will die a traitor in her eyes, she would hate him with every fiber of her pure heart so she would not have to shed a single tear, even for him.
A/N: I think it would be way cooler if Gin had infected the hougyoku and so it destroyed Aizen. Gin is too awesome to not screw Aizen over from beyond the grave.