"No lightning today? What's the matter, afraid I'll redirect it?"
"Oh, I'll show you lightning!"
Zuko took a deep breath as Azula prepared her attack. Lightning surged around her making her hair stand on end. Zuko saw her eyes shift focus away from him. At the very last moment before her attack she noticed Katara then she fired. The lightning left her fingertips on a direct course for the young waterbender but Zuko ran to put himself in between. He slid into position just in time for the lightning to enter his fingertips. His hair stood up as the energy travelled through his arm into his stomach and back out of his other arm toward the dumbfounded Azula.
Azula's eyes widened as the azure bolt traveled toward her in seemingly slow motion, and then she realized that she should be able to redirect it as well. Zuko could do it so why not her? This was not her first time seeing the technique, she was confident that she'd be able to mimic it. The lightning entered into her outstretched fingertips and into her arm but then she felt a sharp and intense pain in her chest as the lightning jolted through her heart, a grave mistake.
"AARRGGHH!" She screamed. The muscles in her arm seemed to spasm as the lightning passed out her fingertips, exploding on contact with the walls and columns to her left. She grabbed her chest as she fell to the ground writhing in pain. Zuko finally realized what he had just done.
"Azula." He whispered to himself before running over to his little sister.
"Zuko." Katara yelled as she ran after him.
Azula quickly crawled away with one hand always clutching her chest.
"Stay away from me!" She screamed shooting a weak blast of fire at Zuko as he ran toward her. Her aching heart started beating faster and faster as her breathing became more and more labored. Tears ran down her cheeks and she struggled to drag herself away. She was scared, more afraid than she had ever been in her life.
She tried to stand up but fell and rolled over to her back catching one last glimpse of Sozin's Comet passing in the sky above her heart beating faster still. Zuko ran to her side and lifted her head up and grabbing the hand that was clutching her chest. For just a moment their eyes met hers still glistening from the tears. She squeezed his hand back as she slowly closed her eyes.
Zuko quickly looked up and desperately yelled, "Katara!"
The waterbender ran over to him, her hand encompassed by water prepared to use it to heal but hesitated when she saw Azula's face.
"Please, Katara." Zuko pleaded.
She nodded as she put her hand on Azula's chest and the water began to glow. Azula had already stopped breathing but her heart was still beating. Katara could feel her heart beat starting to slow more and more. Slower and slower until it stopped completely. The water bender lifted her hands and hung her head. Suddenly Azula took a short gasping breath and began breathing again. Zuko was overcome with a wave of relief. He never thought twice when he was redirecting the lightning at his sister. He never really thought about how he'd feel had he actually killed her. He's never been good at thinking ahead.