Disclaimer: Of course they ain't mine. Dammit.
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Not very often, but none too rarely, either, Renji would look up across his desk and notice something barely visible pinching Byakuya at the corners of his eyes. It was only a thought, only a memory, and Byakuya was superb at hiding it - but once Renji knew what he was looking for, he could spot it every time.
Well, every time he knew of.
Renji would watch as the hazy recall-face of a tiny, black-haired woman pulled non-existent crow's feet onto Byakuya's skin. She tightened his lips so they crinkled in the middle, little soft lines and ridges that morphed into dry scabs the more agitated he became, until he had to lick up infinitely tiny beads of blood from the holes his teeth had torn there. And gentle as Hisana was (must have been?), she never let him go.
Byakuya missed Hisana, and Renji missed Rukia. It was as simple as that. That's why he could see it – Renji's body echoed every twitch, every movement, in the exact same pattern, though it indubitably showed a lot more in him than in his captain. When he really missed Rukia, when she was off with Ichigo somewhere and not thinking about her childhood friend at all, he might as well have had it written in permanent marker on his bandanna.
Still, as familiar as he was with this process, Renji couldn't watch it in Byakuya for too long. Finally, after five minutes or perhaps ten, he would speak.
"Have a drink with me."
"No."
And that was always the end of that, for the next few days, at least. But Byakuya, despite never saying yes, or even anything more than a single word, seemed to acknowledge the effort; he would relax a bit, and the haunted look on his face would recede, so Renji would always ask.