Look at my other story, various signs, for the movie Secret of the fire nation! It is posted on youtube already, credit goes to the person who had uploaded it.
Disclaimer- I do not own Avatar: The last airbender
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Just when the plan had started to work, Aang was shot hit on the back of his head with a boulder. He flew ten feet away, hitting the wall. Blinking, he saw the image of an earthbender being attack from all sides, guilty for his treachery. But he had done his job, and they all knew that. He had shut down the Avatar, and the fire nation was advancing. Without him, Ba Sing Se would crumble. Aang, desperately trying to stay awake, failed. He went unconscious as blood began to leek through the back of his neck. He had no idea what happened anymore.
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Katara suddenly woke up to the sound of distant shouts and yells. She hurriedly headed out the door to find out what was going on, only to be stopped by two guards.
"Ma'am, you are not to leave this room until further notice, as requested by the Avatar." Katara maddened.
"Well, did he tell you that I choose what I want to do, not him?" And with that, she water-whipped them both, and they fell to the ground. She ran past the bodies, hoping that there was still time.
But she was wrong. Time had already run out.
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Katara ran through what seemed like a series of never ending tunnels. Finally, when she got out of the building, she gasped. She could see smoke coming from the direction of the wall, and shouting all over. She hurriedly ran to the entrance, not even stopping to apologize to the people she had pushed passed. But just when she reached the entrance, her eyes widened, and her heart collapsed. There he was, Aang, on a stretcher, a bandage wrapped around his head. The only holes were by his mouth, nose, and eyes. Everything else on his head was completely covered. She hurriedly ran towards him, tears forming in her eyes. No. That couldn't be. Not Aang. Please not Aang.
But there was no doubt, by his attire and his height, that he was Aang indeed. The medics hurriedly carried Aang to the emergency medic tent, where he was put on a bed. The bandage around his head was quickly but carefully removed, and Katara was confused. His face looked normal, and he had few bruises on his cheeks. That was when she saw a pool of red stains on the bandages. She couldn't believe it, but she knew she had to. Only to make things worse, a doctor came and turned Aang's body so that his chest was facing the bed, and that was when Katara saw the extent of the injury. His whole skull was out of shape, and his head was deformed. There was a large patch of flesh, and inside it were mud, sand, and blood all mixed together to form a clot.
Katara's knees began to weaken; her whole body was shaking. Tears were streaming down her face, and she had not bothered to cry out. She sobbed and gasped, and it seemed like no one in the world was watching her cry. She let her broken heart out through her raking sobs, her face buried in her hands as she knelt on the ground. Aang… not my Aang, please not my Aang. I don't believe it. He's not dead. No… no… HE'S NOT DEAD!
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The sun was rising, and the fire nation was around 100 feet from the wall. Only around a third of the troops were alive; thousands had been murdered by war balloons, trebuchets, and firebenders. Although the fire nation soldiers were within range now, most of the troops didn't attack; they had lost hope. Only a few, like Pakku, Sokka, and Haru, were convincing them to fight. Few did, only to get nasty burns as a result. The soldiers began to retreat, back into the city. There were thousands of corpses lying on the ground, as the trebuchets launched even more fireballs at the wall. Rocks crumbled, earth rumbled. Ba Sing Se was falling. Thousands of innocent lives had been lost already. And thousands more will fall.
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Aang.
Avatar Roku?
Aang, you must stop this battle.
But how? There are just too many. And even if I did trigger into the Avatar state, they could kill me.
Yes, their plan was flawless. They destroyed the wall at night, and when the sun is up they will invade Ba Sing Se, the time when they are at their most powerful. But there is a traitor in the city, and you must find him and kill him before it gets too late.
But how? I can't even move! And he must have a lot of henchmen working for him; that's how the soldier attacked me! The fate of the world is in my hands, and I failed them. I failed them all. Sokka. Appa. Momo. Pakku. Haru. All of the innocent people who just wanted a peaceful life. And I failed Katara.
No you didn't. You may not know, Aang, but you had given Katara hope from the moment she had first met you. And she still believes in you, right at this moment. She still believes that you will save the world.
Katara…
Aang, me and the past Avatars will use all of our powers to help you win the battle. But for now, we'll give you the strength to talk to her.
But why? What would I say? I can never forgive myself for what I had done.
You will know. But for now, the world still has hope.
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Aang slowly opened his eyes, and although he was facedown on the mattress, there was no doubt that the battle was bad. Shouts were coming from all over the place, and he could tell the fire nation was getting closer.
But then all sound became farther, and farther, until it disappeared completely. Now, there was only the sound of one person, cries ringing through his ears.
"Katara…" Aang , managed to whisper, loud enough for the waterbender to hear. He could hear her sobs coming to a short stop, although she was still chocking in her own tears.
"Aang?" she said disbelievingly.
"Katara… it's me… please…" Katara quickly went by Aang's side, and his head tilted a bit so he could see her. Her eyes were red and puffy, and her bottom lip was bleeding because she had bit it too hard, trying to hold back her tears. Her face was wet, and so were her hands.
"Please what Aang?"
"Please… heal me…" Katara panicked.
"But I had never healed something that serious before!" Katara was holding back sobs again. Aang used all his strength to reach for Katara's hand, and squeezed it gently. And this was the last thing he said before passing out again.
"I know… you can do it."