never learn much about Hisana, at least in the anime, or her
relationship with Byakuya. My take on the start of things. Inaccuracies are probable.
He hated it. The filth. The children with their hollow eyes. The women in gaudy clothes and the drunkards who chased them. The smell of it, like sweat and blood and alcohol mixed together.
The only reason Byakuya could imagine that his captain had sent him here was to disgust him. But no, Ukitake didn't do things that way. He was probably supposed to learn a lesson of some sort. Respect for the common man, that kind of thing. It wasn't working. Byakuya's contempt for the inhabitants of Rukongai hadn't lessoned one bit since he'd come here. If anything, it had only intensified.
He sighed to himself as he patrolled the crowded streets at a leisurely pace, ignoring the wide-eyed, awed stares of the commoners at the sight of a true shinigami among them. It was only for a night. One night he was assigned to patrol this place, then he could return to the Court of Pure Souls. He could survive one night in Rukongai. Even if he dared not sit down anywhere.
Byakuya halted. A pair of children, either very daring or simply very foolish, were trying to sneak up behind him to touch his zanpakuto. He turned and fixed them with the coldest glare in his repertoire; the children yelped and fled. Ukitake had always said that that look could chill ice if Byakuya worked on it long enough. Undoubtedly a few more nights in this place would see it perfected.
About to move on, he hesitated as the sight of a gathering crowd and the twang of a samisen attracted his attention. The commoners were crowding around a small, dark-haired woman who knelt on a cushion by the riverbank, head bowed, stroking the samisen in her lap into a strange, mournful tune.
He frowned and elbowed through the crowd, not bothering to spare any manners, until he stood in front of the woman. "Public displays for money are not allowed," he began, then stopped as the woman lifted her head.
"Oh, I'm not collecting." Her voice was soft, melodic, and her dark eyes were so large in her thin, pale face that she should have appeared gaunt, only she didn't. Those eyes looked at him curiously, directly; whereas anyone else's gaze would have skittered to the side, hers held his. She wore a simple, unpatterned yukata and her hair was unbound. Another commoner, sitting in the dirt.
Then she began to sing.
"In the autumn fields
Mingled with the grass
Flowers are blooming
Should my love, too, spring forth
Or shall we never meet?"
She strummed the samisen as her voice drifted away on the last note, and Byakuya found he needed to catch his breath.
When the crowd broke up and scattered—no one left money; she had not lied—he remained. The woman idly strummed her instrument, and when all had gone, to their work or their homes or their favorite taverns, she looked up at him again and smiled. "Yes?"
He swallowed. "Will you sing it again?"
Her head tilted slightly to the side so that a long, dark lock of hair fell across her face. "What's your name?"
He sank to his knees in the dirt before her. "Kuchiki Byakuya."
"Kuchiki-san." She smiled again. "My name is Hisana." And she sang.
When morning came and Byakuya returned to the Court of Pure Souls with only his zanpakuto and a crumpled piece of paper, marked with clumsy kanji, tucked into his sleeve, he went to meet Ukitake in 13th Division's halls. "So tell me, my friend," Ukitake said, slinging a friendly arm around Byakuya's shoulders (a gesture he knew Byakuya hated). "What did you find out there in Rukongai?"
The paper in his sleeve. Hisana's lyrics. "A promise."
His family would despise the very thought. Every shinigami in thirteen divisions would think he'd run mad. He didn't care. Byakuya was going again—willingly—to Rukongai, and he was bringing back a wife.