It wasn't as if he hadn't the slightest interest in her.
He watched her move about, light on her feet and perfect in posture and poise. She was quiet, dignified, careful in her actions and such, meticulous as not to make a mistake and shame herself in his presence. He was the patriarch of the Kuchiki clan, after all. And she was his adoptive sister, a Rukon kid adopted into a noble clan that she would never had had any chance of being in, had it not been for her late sister. The one she never knew.
Byakuya was busy with paperwork taken home to the Kuchiki complex, being done quickly and silently from his chair in the corner. Rukia was currently moving about, retrieving a book to read in the chair on the other side of the room. It was the lounge after all; Byakuya would normally have chosen his office if he had not felt that powerful sense of nostalgia by looking at his technically sister-in-law. The aristocratic lord of the Kuchiki clan was always in motion, always keeping himself busy with taking work home and taking Abarai's half as well when he needed it, just to keep himself from settling within his own thoughts. He couldn't allow himself to settle in his own thoughts, for that was when he settled down into his own memories.
Byakuya Kuchiki couldn't allow himself into those memories of calmer, happier times with Hisana. If he did, then unneeded emotions would surface once again and he would be crippled by them, instead of remaining the cool and emotionless Captain that he needed to be. His memories should remain for late at night, when he was alone and could drown in his own misery in peace. The man may have been as cold as granite, but that didn't mean he was granite through and through. It had worked for him so far, and he could keep his steel and unmoved mask on and his emotions for later, when he could suffer them in peace.
Rukia was quickly becoming a point of obsession for him. She looked almost exactly like her sister, though possessing less elegant features in some ways, and not quite as tall. But she had the same face, the same hair, and the exact same violet eyes that he had adored on Hisana. Her laugh was the same, though Byakuya himself didn't hear it often when he was around. She had the same inherit kindness, the want to help others. And she was growing more and more like his late wife every day.
It was maddening.
Rukia herself wasn't helping either, but not because she was being purposefully difficult. Because she didn't know. The young woman hadn't the slightest clue of her effect on her honored brother, and merely went on her way in tormenting Byakuya more and more. The occasional times she called him by his name, Byakuya nearly swore it was as if Hisana were calling him herself. How Rukia attempted to care for her elder brother, merely worried for his well being, it was all too familiar to him and he wanted her to stop. Not that he could openly tell her to stop caring about him, and her not become suspicious. Byakuya Kuchiki was trapped, with the doppelganger of his dear late wife always buzzing about him with no idea of the pain she caused.
He couldn't just love her, either.
A sneaking suspicion had been with him for years now, the suspicion that Hisana's sudden death was no accident. Many of those in the Kuchiki house had nearly revolted when they found who Byakuya took as his wife. A common Rukongai woman, that they saw as both a blight upon the name Kuchiki and as an unworthy tramp merely suckling from their wealth and using the head of the family's heart as a tap. Byakuya had seen how quickly Hisana deteriorated at the end, and all he could suspect was poisoning. Doubtful that he would ever find who did it, considering how many had been bitter over the marriage. Byakuya didn't want to risk taking Rukia as a second wife and having the same fate befall her. He couldn't bear to go through it all again.
Even if Byakuya Kuchiki could have told Rukia of the feelings she had brought back to life within him, could have lived without any interference from other nobility, could have broken his oath to his parents' graves of never breaking the laws again, could have put peace with Hisana's memory…he wasn't sure that she would even love him back. What if Rukia didn't love him after he told her that he felt for her? It would forever change their relationship, and she would distance herself from him permanently. Byakuya couldn't bear that either.
So he would remain silent. Remain silent, and preserve this hellish serenity that he endured daily. He would play the guardian to Rukia, the love that was barely out of his reach. Byakuya watch over her and if he could not love her, then he would protect her with his life.
Chancing a glance up to where Rukia had been sitting, he noticed that she had fallen asleep with her book. It was lying across her lap at an odd angle, no doubt bending the pages. Lo and behind, it was one of Byakuya's personal favorites. He could have sworn that she was paying special attention to his favorite things recently, cleaning them of her own accord or reading through his own personal favorite books and documents. Noticing that his paperwork had been done for a very long time and that he'd been continuously writing and then meticulously correcting the B in his first name, Byakuya sighed lightly and set the paperwork aside before he mutilated it any further, standing lightly. Quickly closing the distance to the chair Rukia was slumbering in by a quick and purposeful step, Byakuya reached down and picked up the book to straighten the slightly bent page she had been on. He picked up the volume and examined it further, realizing what book it was and what page she was on. His eyes lessened to the normal emotionless state, before Byakuya looked back down to Rukia sleeping peacefully, oblivious to the burgeoning affection centered on her by the elegant patriarch that put up the image of constant disappointment or cool indifference. Ever since the Aizen debacle and his forcedly uncaring attitude about it all, there had been a sort of regret in his soul that Byakuya did not appreciate. There had also been what he perceived to be as a debt of guilt that he owed her, though Byakuya Kuchiki would never admit to guilt.
Another slight glance was paid to the volume in his hand, the page still held open with his thumb. Byakuya returned his eyes to Rukia, reaching out slowly and brushing the very tips of his fingers along her face, brushing back her hair almost lovingly.
"Wretch," I cried, "thy God hath lent thee - by these angels he has sent thee. Respite - respite and nepenthe from the memories of Lenore! Quaff, oh quaff this kind nepenthe, and forget this lost Lenore!" Byakuya recited quietly in his natural austere nature, chancing a slight brush against her the warm skin of her cheek. In her sleep, Rukia turned her face and laid her cheek fully in his cool palm and Byakuya recoiled, moving his hand from under her head slowly as not to wake her. She didn't move after he retreated from her touch, and Byakuya stared down at the embellished volume. Works from a Living World writer long dead, one that he had particularly enjoyed reading in his times alone after his own Lenore's passing.
Setting the volume back on the shelf, Byakuya pulled down the cover of the chair Rukia was dozing in and let it fall over her like a blanket, before turning and heading out the door of the lounge, moving to his own room to prepare for bed.
Quoth the raven, "Nevermore."