I know it's confusing, but try to get past the gender ambiguity. There aren't that many good female characters in Bleach.
In a cold kingdom, there once lived a happy family. King Ukitake, and his wife and child. The king's first wife, Kaien, had died in childbirth. When the king chose a new queen, he made sure to choose someone beautiful, so that his daughter would have a feminine influence. The new queen was certainly beautiful, thought by many to be the most beautiful in the kingdom. He was called Yumichika. And while the king was alive, Yumichika was loyal and kind, and cared dutifully for the princess.
But the king was sickly. He often went out to defend their kingdom, in the freezing cold, and paid no heed to his doctors' warnings. Then one day, when the princess was still a child, he died. The queen was desolate. For almost two days after the king's death, he sat by his bedside, and screamed at anyone who tried to enter the room or touch his body. Finally, it was the little princess who comforted him, and soothed him, in spite of her own grief. From that moment on, the queen hated her down to her very soul.
The princess was somewhat homely as a child. But she had dark, raven hair, and pure white skin, like freshest snowfall on a moonlit night. Her given name was Rukia, but most of the kingdom's subjects called her Shirayuki Hime, Princess Snow White.
In the queen's grief, he turned all his attention to the pursuit of beauty, which King Ukitake had often praised him for. In his mind, it was the only thing that he had over Princess Rukia, his one remaining mark of Ukitake's love. To that purpose, he acquired a magic mirror, which would tell him unfailingly whether he was indeed the fairest in the kingdom.
Princess Rukia grew, and soon her gawky figure evened out, and though she was still slim, she soon had a pleasant shape. She also remained small, petite, yet always a little indelicate, or perhaps masculine. It was likely this aspect which blinded the queen's eye for so long. Her eyes became large and black, and undoubtedly charming. Her mouth remained small, like her nose, and her cheeks took on the gentlest flush of pink. Before anyone realized it, she had made her way into puberty, and no one would contend now that she was beautiful.
Queen Yumichika gradually became aware of Princess Rukia, but remained a dutiful mother, at least in appearance. Then one day, the queen stood before his magic mirror, and asked the same question he always did.
"Mirror, mirror, in my hand, who is the fairest in the land?"
The vague face behind the glass replied in its deep, distorted voice, "My Queen. You are the fairest here, so 'tis true. But Snow White, by a thousand times, is fairer than you."
Yumichika's face drained of color. For him, it was as if he had been told his existence was meaningless. That was the end. That was the end of Rukia's peaceful existence in the same castle, in the same world as him. She needed to suffer, and not just for this, but for her original crime, the reason Yumichika could never forgive her. That she had loved Ukitake as much, or more, than he, and still had accepted his death. For this, Yumichika felt he might never be satisfied, no matter how much pain she suffered.
So Yumichika made a plan. And he called forth the only person who was suitable for the task.
On a chilly day in autumn, the royal huntsman was called before the queen. He knelt before her throne and dutifully bowed his head. "Your Majesty. I have come as you summoned me."
Yumichika smiled. That smile now only barely concealed the pain and hate. "It's nice to see you, Renji. You don't come around to the castle much these days."
The redheaded huntsman looked up hesitantly. "No, Your Majesty," he said slowly. "Princess Rukia and I are no longer children. It would not be appropriate."
"Well, there is some truth in that. But I hope that you and I, at least, can become good friends after this."
Renji looked up with confusion. "Your Majesty?"
Yumichika smiled like the cat that got the canary. "I have a task for you, Huntsman."
Renji lowered his head dutifully again. "Yes, Your Majesty. Whatever you wish, if it is in my power."
"Kill Snow White."
The huntsman froze. Slowly, his gaze rose to meet the eyes of the queen, disbelief streaked across his features. His breathing grew labored, his lips parting as he continued to stare, unable to find his voice. He knew, as did all present, that the queen was perfectly serious. "Your Majesty," he said at last, in a quiet, plaintive voice. "I…I cannot…"
Yumichika's smile had not faded. "Hm? Interesting. But you must be aware that if you say that…" he flicked a single finger forward, and two men stepped from the shadows behind him. "…my brothers may take issue. In fact I'm almost certain they will. Right, Kenpachi, Ikkaku?"
The infamous brothers of the queen stepped forward. One, at least eight feet tall and covered in scars, glared down at him through one eye, while the other was covered with an ominous eye patch. On the queen's opposite side was a muscle-bound man with a shaved head, and a wicked grin that almost reached his ears. He tapped his long, three section spear-staff against his shoulder as if itching to use it.
The huntsman trembled. He was not a coward, but these two men were clearly out of his realm of understanding. They only craved blood, for no other reason than because they loved to fight. He did fear them. But they were not his problem right now.
He resolutely lowered his gaze, trying to quell the trembling in his hands. "Even so, my queen, I…"
Yumichika's smile faded for a moment. Then it came back with even stronger fervor. "You know, somehow I really hoped you'd say that." He rose gracefully from his chair and lithely approached the kneeling Renji, knowing he would not run. The queen was an expert in demon magic, and as he walked, something began to glow with azure light around his left hand. "You will take Princess Rukia into the woods. You will slice open her chest. You will bring me her heart. And you will be happy to serve me in doing this."
Renji's eyes opened wide in panic, and he belatedly thought to run. "No…Your Majesty, please…"
Yumichika yanked his head back by his hair, and raised his left hand over him. "Open your eyes. Keep them wide open." He grinned. "I can't tell you how many times this spell has fried someone's brains, when they weren't paying attention." He covered Renji's face with his hand.
Rukia gasped awake in her bed. She thought for sure she'd heard a scream. Her heart pounded for a few moments, and then eventually slowed. "Maybe it was only in my dream…"
She yawned and stretched, rising to see the sun shining in her window. She smiled. The past few days, she had been cooped up in her tower, so little things got her through the day. Still, it was odd. Usually, when the queen was angry about something, he tried to cover it up for a while, but eventually took it out on Rukia. This was the first time the queen had forbidden her to leave her room. Rukia was somewhat concerned. Yumichika tried to hold in a lot of things, and though Rukia often tried to get him to talk about it, she got the sense that she wasn't the right one for him to talk to.
She went to her window, letting in the brisk morning air, and got herself dressed. No sooner had she done so than she heard a knock on her door. "Yes?" she said.
There was a pause. Then a soft voice, "Rukia."
Her face brightened. "Renji! How did you get in here?" She immediately ran an opened the door, trying to be harsh with him, but just too happy to do so. "You're going to be in big trouble. You c-…Renji?"
Renji looked as if he hadn't slept. His eyes were bloodshot and avoiding her gaze. He had some stubble coming and his cheeks were sunken.
"Ren…ji?" Rukia asked softly.
Finally, he looked at her. He smiled, but it was one of the saddest smiles she'd ever seen. "I've come to bust you out for a while."
Still unsure, Rukia slowly shook her head and murmured, "I can't. I don't know what Yumichika would do to you if I did."
"It's all right actually, I was just joking," he said, his gaze growing distant again. "I talked to him for a bit. He says it's fine." He hesitantly looked at her again. "All the same, we should go now, before he changes his mind."
Rukia felt a deep, underlying fear somehow. But she didn't want to miss a chance to talk to Renji, so she grabbed her cloak and some thick boots and followed him out of the castle. Soon, she was starting to wonder where they were going. He wasn't saying anything, or laughing and joking as he normally would, just walking steadily toward the woods. He was walking at his pace too, not hers, so she was having to jog sometimes to keep up.
"Renji," she said, at length. "You can talk to me if something's wrong. We don't have to come all the way out here."
"It's not that," he said. Now, he seemed to have dropped his earlier attempts to seem civil, his expression dreadfully pained and his tone dark.
"Renji…" Rukia murmured. "Then please tell me why you look so sad."
This only seemed to deepen the lines of pain over his face, and he did not answer. They entered the woods, and still kept walking. Rukia was silent then, deciding that Renji would answer when he needed to, and if just being with her was helping him somewhat, then she would do that. But suddenly, Renji stopped walking.
He stood there silently for many long seconds, and Rukia was a little behind him, so she couldn't see his face. She was about to speak when he moved. With a trembling hand, he reached for the knife in his belt.
Sudden fear shot through Rukia's chest. Renji had taught her most of what she knew about fighting and hunting. Seeing him draw his weapon was nothing new to her. So why was she so terrified? She had to ask herself, because it didn't make any sense. It was Renji. No matter what was wrong, he'd never do something to hurt her. Never. Never. So why…
"Rukia…" Renji said. His whole body was trembling, and it was clear he was speaking through gritted teeth. "Run…run, please, Rukia. Run, and don't ever come back here…run, Rukia…DAMN IT, RUN!"
He whirled around with his knife in a gutting grip. The whole scene was frozen for an instant. Renji's frightening voice had caused her to take several steps back, but she was in momentary disbelief. Both that he had turned his blade on her, and more importantly, at the desperate sadness in his eyes as he did. A tear dripped down Rukia's cheek. She knew in an instant there was nothing she could do.
She turned and raced away from him as fast as her legs would carry her, which was still not fast enough if he was serious. Fortunately, he didn't seem to be following. Still, her legs would not stop. She sobbed loudly as tears streamed down her cheeks.
She had lost her only friend.
She didn't know what had happened to Renji, but whatever it was, the result was the same. She had lost her home, her best friend, her only family, although in the back of her mind she was starting to suspect what had made Renji act this way. It was a bit suspicious how easily they were able to leave the castle. This certainly wasn't Renji's own nature. The pain on his face. It was terrible. Rukia's heart felt like it was being torn apart over and over, as she kept picturing the pain and fear in his eyes.
Please, she prayed to herself. Father, protect me. I don't want to die.
Shameful though it was, and much though she was terribly worried about Renji, she had never felt fear like this before. She couldn't stop crying. For a sheltered girl like her to have her life threatened and then lose her home in one instant, her mind could barely cope. She just kept running and running, scratching her legs as her dress was caught in thickets, scratching her arms and face as she ran through low branches. Twice she stepped into swamp water, not even feeling the cold at first. She might have been running a full hour. But finally, as her tears started to fade, along with her strength, her consciousness started to as well. Still sobbing slightly, though she was stumbling and her eyelids drooping, she crept underneath a fairly dry, hollowed-out fallen tree. Emotional and physical exhaustion soon took their toll, and brought her to an uneasy rest.