Proximity
It's a matter of proximity.
Ukitake has been around a long time, and he has had the time to learn what he truly wants from another person. He has also had the time to learn what he does not what from another person, and this girl is so filled with those things that he can't help but know better. But it's late and it's cold outside, and she's shivering as she sits next to him. He knows that she'll take it the wrong way if he drapes his haori over her, but he does it anyway because he doesn't like to see anyone uncomfortable, not when he can do something about it.
From where she's sitting she smiles up at him, a rosy blush across her face. So trusting. Ukitake looks down in her eyes and understands just how easy it was for Aizen to do what he'd had to his subordinates, that Kiyone was no more immune to manipulation than Hinamori had been. All it takes is an offer of kindness, a nod of approval, and a sense of belonging. Faith given in return as easily as a haori, loyalty so simple like the stroke of a finger across a flushed cheekbone. So little received, and with that he could use her to move mountains.
Ukitake wonders if she knows how much that frightens him for her.
If Kiyone had been Hinamori, if he had been Aizen, if a thousand plans that he and Shunsui had made had not gone the way they had hoped, perhaps things would be different now. Perhaps he wouldn't be content in his lot in life, that sitting next to a girl on this wall wouldn't be enough, that the simple fact that the night was calm and there was no trouble to be found when they patrolled would have not left him satisfied. Perhaps he too would have looked at the person next to him and wondered just what he could make of her if given the time and the proper motivation.
A momentary lingering of his touch, too long for how he meant it.
Kiyone closes her eyes and leans into his fingertips, a tiny motion but one that he understands. Giving, willing, loving… She has the loyalty of a fukutaicho, if not the raw strength, but what she has she gives to him. There's a reason that she's never left his division to transfer to another, that she doesn't take anyone up on offers for dinner, that she patrols with him even though he was scheduled to do this round alone and sits these late hours of watch at his side. She is his, and he knows this, and as he drops his hand Ukitake is firm in his decision to push away any temptation that comes with it.
Large pretty eyes look up at him. It would be so easy to close the distance, to cross the line, to break down the barrier. It would be so simple to turn her into anything he wanted. So very simple, Ukitake thinks sadly.
Fortunately that's not what he wants from another person. Blind ignorant faith had never been his thing, and he prefers to earn what he is given. So when she leans her head against his shoulder, he lets her, but when she falls asleep at the very end of their watch, his hold on her is simply for support so that she doesn't accidentally tumble off the wall. When he flashes them both back to their division, it's because it's faster this way and Kiyone is grumpy in the mornings when she's tired. He only smiles as the sleepy girl snuggles into her bed (not his) still wrapped in his haori. After all, what she has to offer isn't what he wants, and he knows this. He knows it. He is not Aizen and he never will be the one to lead Kiyone down a path that they should not follow. Any tiny wavers on his part are simply inadvertent. It's just… a matter of proximity.
Ukitake slips out of her room and leaves his subordinate in peace.