Zuko didn't know it would be his father, stepping out to duel. He couldn't hear his father's words, the sounds were nonsensical garbled noises that held no meaning. But the disappointment and cold fury that lay underneath them, that he could hear. Pure terror had swallowed him whole the second he'd seen his father's face. There was nothing to stop the Firelord's rage now.
"Father please, forgive me" The boy half sobbed and half begged, his voice cracking and his eyes felt as if his woes had alighted into biting little fire spirits. The floor was blurred and he couldn't stop shaking. Ozai said something else. Zuko looked up, just in time for him to get struck in the face with fire. A tortured scream escaped the thirteen-year-old boy as he fell back, the force of the blast shoving him like a rag doll. His back hit the smooth and unforgiving tile floor. The impact would probably leave bruises. But that wasn't important. The only thing on the young prince's mind was his burning face. He was never one that cared about pretty faces, as they were often covering cruel monsters in his experience. He didn't really care all that much about his appearance. He wasn't worried about how he would look after. He was writhing in agony. It hurt. Pain, the world didn't even begin to fathom how awful it truly was. The stench of burning flesh was inescapable, the heat was absolutely unbearable, and the smoke coiled like venomous vipers, diving into his lungs. The flames attacked his hair and scalp before it was forced down, leaving the burned heap that was a boy exposed for the world to see. Now that the fire was gone the blood rushed out, the Prince still trying to gasp for air while his esophagus and lungs filled with his own boiling blood. He had only one eye, too fogged up by the trauma to really see. It was a huge kaleidoscope of blurring colours. He couldn't make out any voices through the roaring in his ears. He couldn't feel the hands grabbing at him. But he could feel the cold, the slow drain of his senses falling away. Then a voice cut through the thick veil, a trembling muffled whisper;
"Brother, please don't leave me" Zuko tried to reach out, he tried to hang on. But he was only human and his struggles did nothing. Death took the boy, carrying his spirit off to its new home. The Prince opened his eyes. There was no pain, he felt fine. Light even, as if a weight had been lifted from his shoulders. Around him was a beautiful world, trees of every shape and size with leaves of so many colours. And a young man sitting, not facing him. Zuko knew him, an ache struck his heart. He knew that man. The boy walked, cautious and quiet. As if snapping a twig would make the man disappear.
"Lu Ten?" Zuko dared to whisper, as every memory came flooding back. He was in the spirit world. He was dead.
Azula usually enjoyed her brother's suffering. He was weak, pathetic. A smile had been firmly glued to her face until after the fire blast. Zuko didn't get up. The smile slipped off, and with it the mold. The mold that made her Ozai's perfect little heartless soldier. Zuko was her brother. Her big brother. He was there to protect her from the nightmares and what lurked in dark corners. He boasted about how his little sister was going to be the most talented firebender the world has ever seen. He looked out for her and she pushed him away. The eleven-year-old bolted out of her seat and ran down into the ring.
"He's my brother! He's your son! How could you!?!" She screamed at the monster she called father. The only things that existed to her anymore were herself, Zuko, and that heartless monster. She gazed frantically down at the crumpled bloody heap that was her brother. There was too much blood, the burn was too deep, too damaging. He wouldn't make it. As a very practical and logical girl she knew that. But she wasn't willing to accept that, her mother was gone, along with her cousin, but she couldn't lose her brother. She couldn't lose Zuko. She crouched down trying to lift his head. The tears welled up in her eyes. "Brother, please don't leave me," she whispered, the salty tears growing fat. Each heaving and shaking breath grew shorter. Then they stopped. Panic grabbed ahold of the eleven year old. She shook him. She felt as if she were three years old again, pulling at her brother sleeve and begging him to keep the monsters away. He couldn't leave her. "No! No brother, please!" She could feel it, his life leaving. Greif joined the ranks with rage. With tears marching down her face like soldiers of sorrow she stood up. She whirled around to face her father, her corrosive gaze boring through the air. Her jaw clenched fiercely. The air around her was hot and sizzling with energy. She shot two fireballs, straight to the floor. They were blue, the flames were gorgeous to any on-looker but they were also hotter, more dense, and more powerful. Blue for her sorrow, for her cold-blooded fury. Azula noticed uncle, his face aged with many more years than he had experienced, his eyes held with more weariness than they should have. He had lost his son three years ago and he now had lost the boy who became like another son to him. From the hands of his own younger brother no less.
"Azula,-" his words were white noise. She hurled blue flame over her shoulder, aiming to kill. That monster wasn't a father, he wasn't a suitable lord, not when he could murder his own eldest. Three years ago Azula thought it had only been a joke. To scare her frightful brother. She'd taunted on and on 'Dad's going to kill you!' and now that promise had born fruit and her brother was dead by her father's hand. Why had she said that? Why had she been too naive to understand how cold-hearted her father was? Why had she let him trick her into being his cruel little soldier for so long? She didn't know.
Princess Azula was exiled for her treason. Attacking her Firelord in the midst of so many loyal nobles. The girl became coldhearted towards anyone who paid loyalty to the Firelord. She left with the promise to avenge her brother, promising to leave only blood and ashes of all the people who had watched and done nothing.