Timeline: Set in the future, after the Hueco Mundo mission. Speculation and spoilers up to the current manga (at least ch. 285).
x
It is known in the Kuchiki house that Lady Rukia did not return unscathed from the Hollow World.
In body, she is well. Her will is as focused on the battle against Aizen Sousuke as ever. Still, her feet shuffle restlessly along the corridors, and more than once, she is caught staring out of windows into the late autumn sky, like a bird denied flight. She picks at her food, even when dining alone. This is a warning sign to everyone in the house.
She comes to the estate to sleep every night, murmuring that she wishes for solitude. The division quarters are crowded, she says. The older servants whisper how, in the beginning, she'd bunch her futon in a corner of her room and nestle there, in fear of all the open space.
Captain Kuchiki makes no comment on his sister's situation. Everyone expects this to be so.
In any case, they are both gone a great deal. The war will be upon Soul Society any day now, but Lady Rukia seems to already mourn those who are yet to be lost. She carries out her duties with exemplary form, but her eyes look past the living in the way most warriors come to know: it is the fallen that she sees.
It is not like her; but Kuchiki business stays within Kuchiki walls. The hearsay is quelled.
x
She sleeps, but her thin slumber could be punctured by a whisper. Thus, he makes no sound as he enters the southern sitting room, with its windows opening into the garden.
Her aura flickers and gleams, although she should be at rest. She was always steady, stealthy; he took pride in her effortless control. Now, she cannot calm herself. He cannot hear the names she speaks in her sleep, not through the two rooms between them. He has no wish to, although he knows they would be familiar to him, too.
The moon draws a stroke of light across the room. He seats himself in the shadow. Then, all but gingerly, he begins folding the errant tendrils of her aura into his own. She shifts, but does not waken. He is careful.
He remains silent and still until she slowly, slowly settles into a deeper sleep where the dreams do not come.