At first, Aizen decided that it must have been artistic appreciation which made him feel the lack of her presence. He had crafted her, after all; made her what she was. He missed her as he would miss a work of art or a tool.
Then he considered that perhaps it was her enthusiasm that he missed. Or perhaps her willingness to do anything for him. Yes. It was natural that he would miss that. Any sensible person would.
She was a sweet child, he thought vaguely, and made himself put the thought away with the memory of her smile.
---