and for no other reason
Aizen waited. The curtain of fire blocked his purely physical view of the battlefield to some extent, but he had many other ways of seeing beside the purely physical.
He'd expected sound strategy from Yamamoto, and he had not been disappointed. Prepare the battleground, separate the enemy forces, and block Aizen himself from using his zanpakutou. (Or at least, what Yamamoto knew about his zanpakutou.) While he hadn't necessarily predicted exactly what tactics Yamamoto would use, the strategy as a whole was unsurprising.
Aizen had never got anywhere by underestimating his opponents, and he had no intention of starting now.
So he watched, and he waited: there were other things in preparation, after all, other matters in train, and some of them might be about to surprise Yamamoto very soon, and in the meantime it was always interesting to observe the reactions of other people.
It was because he was watching in ways other than the purely physical that he saw her coming before anyone else on the battlefield did. Her presence was such a familiar thing that he could almost have smiled. Her spirit ribbon was a delicate fragment of red silk that he could have twisted around his fingers (as he had so often in the past) and laid against his cheek.
Little Momo-kun. How nice, how pleasant, how surprisingly warming to see her again.
Ichimaru made some sort of sliding, snide comment about her presence, and Aizen answered in neutral words that gave nothing away. Even if she was nothing to him and never would be, and even if disposing of her had been an urge towards tidiness rather than anything else . . . well, it was always a mistake to show anything private to Ichimaru. Even an urge for tidiness.
In that part of his mind which he reserved for the systematic evaluation of potential resources, he was forced to admit that she had survived and grown in a way which he had not thought possible. It would be . . . convenient, yes, that was a good word for it . . . if he could find some use for her after matters were sorted out. He had always disliked waste.
Harribel's fraccions played out their little dance with their pet, and he observed Momo-kun's fall.
Poor girl. She really had tried so hard. It was a shame for her to be suffering like that. If he had simply dealt with her more effectively a few months ago, she would be at peace now. His fault, he admitted it.
But in another part of his mind, he saw the red flutter of her spirit ribbon, moving as slowly and perilously as her gasping breaths, and he hoped that she would last just a little longer, until he could give her a moment of his time and find a use for her.
Perhaps she could be strong enough for that.