A dark ritual goes awry and now the great Spirit of the Dark walks the earth once more. His power is great, and he seeks only one thing: Vengeance upon the one who imprisoned him centuries ago.
Shinbei grew bored once more, and approached the Avatar for help. He asked the Avatar to give him a task, something to do, in order to alleviate his boredom.
Arventi would never have given him the response he received. Arventi had infinite patience, and more than enough wisdom to know that he should guard his words more carefully.
But Avatar Soren, for all his power and wisdom, was still but a man, and one out of patience from having spent all day negotiating a treaty between a particularly stubborn pair of Earth Kingdom satrapies. He was in no mood to waste his time occupying his petulant brother's interest, and so he snapped, "Go find someone else to entertain you, Shinbei."
And so he did.
He had mortal servants, of course. All the Great Spirits did. Some were priests and zealots who had devoted their lives to serving their creators. Others were gifts from Kings and Lords, an attempt to appease and appeal to their patron Spirits. The Great Spirits had little use for these servants, but they graciously accepted their offers and set them about little tasks that they could perform in an instant-tasks which would sometimes take a servant the remainder of his life.
He summoned one of these servants to him, a man named Oni, and then bent over and pried off the servant's face. There was nothing malicious in this; he would return it soon enough. He removed his own face and placed it on the servant's head for safekeeping, and donned his servant's face.
Wearing this servant's face, he walked among the mortals and lived among them, trying to extract amusement in this way. He was a wily trickster, and so those he spoke with never had any idea who they were truly speaking to.
In the guise of a man, he was exposed to pain, anger, happiness, love and a whole list of other emotions that he had never truly seen in his normal life. True, the Spirits felt most of these things; but these humans felt them so strongly, and so rawly, that they were almost unrecognizable. Although he could not feel them himself, he basked in their projected emotions.
More and more often he returned to his servant, and wore the man's face for longer and longer periods. Mortal life and its emotions were addictive.
And then one day, he left his face attached to Oni's body, and then did not return. Oni waited, for years and years, until finally he realized that Shinbei was not coming back to restore his face. he left then, and began walking the world, terrifying men wherever he went. They say he is still walking, to this day.
Shinbei's addiction to human emotion had grown far beyond the point where simply experiencing it vicariously could sate him. Instead, he had taken to stealing faces when they were full of emotion, and feeding off of them, sucking all emotion from them until they displayed a dead, emotionless expression.
He stalked up the length and breadth of the land, and wherever he found emotion, he took it. None were safe from him: men, women, children, all were taken. Thousands of families found their beloved ones lying in the dirt with no face. The people whispered amongst themselves that a monster was loose in the world, and would continue taking its prey until it was slain.
Great hunting parties and mighty champions were dispatched to find and slay the great beast, but they were all met with failure. If they found anything at all, they either returned without a face or were never seen again. The greatest bounty the world had ever seen was offered to the man who could bring in the body of the face-stealing monster.
All of the Great Spirits knew that something was wrong. Whatever this face-stealer was, it was not of their creation. Perhaps it was a creature from the darkness between the worlds, which had somehow slipped into this land. Perhaps it was some small shred of chaos that had escaped their notice when they were shaping the world, that had taken on its own form. Never did they imagine for a moment that it could be one of them.
And so they would likely never have discovered Shinbei's secret, if he had not made a fatal error.
It was a pale, moonlit night, and Shinbei was slipping across the icy wasteland of the North Pole, in search of a face to feed on, when he saw a beautiful woman of the Water Tribe. She was walking alone, near the outskirts of the city, and the joy in her face made Shinbei's stomach howl. He needed her. And he decided right then that he would have her.
If he had known exactly who she was, he might have hesitated.
As Aang landed on the temple grounds, snapping his glider shut. Koh was here, he somehow knew. Waiting for him somewhere in this place.
He walked slowly through the ruins, keeping an eye in all directions. Koh could slip through a shadow undetected. He would need to be careful to avoid being ambushed.
Aang stepped into a garden area. Once this would have been a beautiful room, with flowers and trees growing by a flowing stream. Now the stream was blackened and foul, and the gardens were overgrown with gnarled, twisted weeds.
With a roar, Koh burst out from the shadows behind the young Avatar, but Aang had been expecting him. He set his stance and brought up a column of earth behind him, blocking Koh's approach.
Koh skittered along the column's side, rounded the corner and then lunged once more, but Aang was already waiting for him. He bent the stream up out of the riverbed and looped it around himself, hitting Koh in the side as he struck. The force was enough to shift even one as large as the Facestealer, and he went sailing through the air to land on the other side of the garden.
Aang took the offensive, pulling small shards of rock out of the stonework and sending them flying towards Koh, filling up the space between them with quick-moving chunks of earth.
Koh's lids slid shut, and when they opened once more he wore no face. Instead he had a gaping maw, and with a powerful exhalation out of that pit came a cloud of darkness. The rocks were swallowed up by it, and then when the cloud vanished they had disappeared too.
Koh darted across the garden, leaping from tree to tree, never staying in the same place for more than a moment. Aang stood in a guarded stance, waiting for him to make his move. This place was saturated with negative energy. The elements reacted sluggishly, and with much less precision. And he had a feeling that it was as good for Koh as it was bad for him.
A thread of darkness lashed out from Koh's mouth, cracking like a whip across Aang's shoulder. Aang stumbled, and another whipped out, catching him across the chin. Koh unleashed an onslaught of dark whips, forcing Aang to the ground and preventing him from focusing long enough to fight back.
Through sheer force of will Aang pulled himself to his feet, whirled his staff above him, and summoned up a powerful wind that shredded the dark strands.
Aang stood, watching Koh. His breath was heavy, and his skin covered in red welts where the whips had struck him, but his face betrayed not a hint of emotion.
"Why?" he asked in a voice dead of all emotion.
"Why?" Koh asked, shifting to a smug-looking woman's face, "Why her? Why take her face, and leave her for you to find? Because I wanted to, Avatar. Because it amused me. Because she was delicious. And most of all, because I knew it would hurt you."
Koh launched himself forward, and Aang met him with a powerful gust of wind. But Koh simply powered through, slamming into Aang and wrapping him up in his coils.
He's too strong for me to handle alone...
Aang could feel the light behind his eyes rising as the Avatar State fought to break free, and he let it.
When Avatar Kuruk found his lover, faceless and limp, he was filled with incredible rage. He swore an oath to find and kill the face-stealer, no matter what the cost.
As he wept over her defiled body, he recognized a familiar scent. It was familiar to him although he had never been exposed to it before, for it was the foul scent left by his youngest brother's passing.
In a moment, everything was clear. He had never before thought to connect Shinbei's disappearance with appearance of the Facestealer, but now that he had it seemed almost painfully obvious.
Now that he knew who he was searching for, finding the facestealer was a matter of child's play. A being of power like Shinbei could not go anywhere without disturbing the world around him, leaving a trail...a trail which was easily followed.
Avatar Kuruk hounded at Shinbei's heels, drove him to ground, and then engaged him in a single combat that lasted for days. The powers of light and darkness fought back and forth, and each threw his full power into the fight. But in the end, Avatar Kuruk cast Shinbei's defenses aside and struck at him directly, cracking him open like an egg and destroying his physical body.
Then, for the first time, Arventi left the Avatar's body, so that he could attend the final Council of Spirits. The Great Spirits called the Creator back to their plane so that It could pass judgement on the prodigal spirit. It ruled that Shinbei would retain his purpose, and much of his power, but that his name and titles would be stripped from him, and that he would be forbidden from forming another another the time came for him to bring about the End Of All Days. He was given new names, names which fit the new identity he had forged for himself.
Ebesh, the Fleshrender, for both the viciousness of his attack and the manner in which he tears the face from its rightful place.
Panei, the Betrayer, for the betrayal of his fellow spirits, of the mortals he was charged with, and of the Creator itself.
And Koh, the Face-Stealer.
And so Koh was once again cast back into the Spirit World, where there were no mortals to feed on. He tried taking from the other spirits, but their faces tasted dry and bitter on his tongue, and they could not sate his desire for emotion.
Wracked every day by pains from his addiction, but infinitely far away from anyone who could feed it, Koh withdrew into the darkness underneath a great tree, and waited.