I do not own Avatar the Last Airbender. If i did .Shyamalan would not be directing the live action movie.
The Lost Son
Lu Ten and his soldiers were searching the forest for any Earth Kingdom rebels. 'You two, check the east, you two, check the south' he commanded. 'Yes sir' they replied and headed off leaving Lu Ten alone. He began searchin the forest. He was very proud to be serving his nation in the war, especially under the command of the great General Iroh his father and soon to be Fire Lord as soon as his grandfather Azulon dies.
As he searched the forest he thought of his family. Of his father who looked up to and hope to make proud by being a man just as great as him, of his grandfather the cruel tyrant he was and how great the world would be once he was dead and the Fire Nation and soon the rest of the world was ruled by his father, he would be the greatest Fire Lord who ever ruled and then he would be Fire Lord. His mother, who died many years ago. Finally he thought of his uncle Ozai, who was always jealous and bitter over his father being born first and being the heir to the throne. His cousin Azula was just as bad, she was only a child and yet he had more of a killer instinct then nearly all of the soldiers in the army at siege at Ba Sing Se. Despite his father's fame Lu Ten did not have the same killer instinct as the rest of his family, he did not like to take a life and tried not to do it unless in self defense. That was such an Airbender thing to believe but still he believed it.
He shared this trait with his cousin Zuko, he was just to kind and gentle, some time he wonder how Azula and Zuko could even be family when they were so different, they were like night and day, fire and water, yin and yang. However Lu Ten managed to hide his mercy from other people or maybe his father had some thing to do with it, either way he did not get the same level of dislike that Zuko got from his father. This showed that Iroh was a better man than Ozai coud ever hope to be. It's a good thing that Zuko's mother loves him so much.
As he walked through the forest keeping his eyes open for rebels he noticed something strange. In front of him was something strange, it looked like a mirage. he move forward to examine it and suddenly the forest surrounding him disappeared. He found himself on a rock surrounded by a vest expanse of sky. In front of him was a giant tree, as he looked closer at the tree he wondered where on was he. he saw what looked like a opening in the roots of the tree that led to a cave.
Seeing no other choice he went into the cave. He went down a flight of stairs into a great darkness where the only light came from the opening he came through. Well, Hello it been so long since I've had guests' came a voice from the darkness. 'Who said that' he asked surprised. 'Me' the voice said. 'And who are you' Lu Ten asked. 'I prefer to keep my name a secret' the voice said. 'Very well then where am i' he asked annoyed. 'You are in my home, the land of spirits' the voice replied. 'You mean the spirit world' he asked. 'Of course' the voice replied.
'Then how did i get here?' he asked 'I thought only the Avatar could enter the Spirit World'. 'Usually but not always, powerful spirits can open doorways between the two worlds, and in someplaces in your world their are weak points between the wall that divide our two worlds, perhaps you came in through one of those weakpoints, sometime they occur in random places at random time for a few days, very few are permanent.
'How do I get back' he asked the mysterious creature. 'Simple, just find another weak point, the one you came through should still be there' the voice said. Overjoy at hearing this Lu Ten said 'Thank you' and began to walk towards the opening but stopped when the voice said 'Stop, I want to show you my face'. He heard a voice whisper in his ear 'Run'. He batted his ear and a small creature like a firefly flew away.
He heard a cripping sound and then heard the voice say from behind him 'Turn around'. He turned around and looked in horror at the source of the voice. It was a monstrous creature, it had the body of a centipede and a white mask like face. It smiled at the look of horror on Lu Ten face and said 'Never trust Koh the Face Stealer'. It face was then cover with an eyelid like thing and then it open it eyelid to reveal it new face, Lu Ten's face.
Without his face Lu Ten became one of the Faceless, victims of Koh who are doomed to wander the Spirit Realm aimlessly forever without identity, without knowledge of who they are, it is a fate worse then death, for they is no end to it and you have no will, no thought, just nothing.