There would never, under any circumstances, be a reason to cross swords with Rangiku.
That was a lie. Of course there would be. He knew that, he just kept the lie up in his mind because the truth was one of the few things that actually tormented him. Just where did she fit into the grand scheme of things, and how would this play out?
He had been good at hiding his meticulous nature. He had never entered a battle he could not win, he had never acted as though anything at all stressed him out much, he had never stepped out of the role and the mask Aizen had taught him to create, he had never. . .
He had never told her the truth.
Of course he couldn't. Not without involving her. And it shocked him, badly, when he realized it was harder to keep a step ahead of her than it seemed. She was never anything but straightforward, and despite the reputation of being a vacuous bimbo, her mind worked in a similar fashion. When he had become taichou, and she had become fukitaichou in her own right, it was difficult to spend time with her as they once had. The conversations they did manage to have were fraught with hidden meaning; he could never get over the way she could ask a question with her eyes. Why are you so cruel? How can you be so flippant? What are you doing?
And it sometimes pained him that he didn't have an answer for her. Not one that would please her, at any rate.
Aizen had been far easier to fend off. In his arrogance, he accepted what Gin told him about Rangiku as gospel. She was useless, thoughtless, prone to obstinacy. Only one of those statements was true. Had Aizen known this, it might have been Rangiku, and not Hinamori, whose faith and devotion was rewarded with a sword through the gut. But Gin had thrown him off her scent. This much, he knew, he could do for her. He knew there was very little else.
He knew that for cold, hard fact on that night when he nearly had taken care of Aizen's Hinamori problem. "I'll fight you from here on," she told him and meant it. And probably expected to kill or be killed. She was not weak in the way that her feelings could dictate her actions. Not always, anyway. Here she made it clear to him where her loyalties lay. He could do nothing in the face of her honesty (which put a spotlight on his dishonesty) but walk away. She could kill him if she had to. But he could never kill her.
So when the plan unfolded and he prepared to follow his master into the heavens, all he could do was turn and tell her the truth. "I could have stood to be held a bit longer. I'm sorry."