Rather short, sorry, but next chapter has a most-awesome fight scene and then a wrap-up.
You're dead. You're dead.
Zuko breathed deeply. Wait, that didn't make sense. He was dead.
Stop breathing.
Right. Except when he did that he found it very uncomfortable and continued to do it despite his efforts.
You're dead. Now open your eyes and look at oblivion.
Zuk opened his eyes, but he did not see oblivion; he registered that he was dead, but he did not feel very different, besides the fact that his heart was beating at an abnormally fast rate. Katara, stirred faintly in his embrace and raised herself slowly to his shoulder, where Zuko could feel the identical, adrenaline fueled pumps of her heart throbbing against his chest. Their eyes were wide and staring, but darkness still encased them like some leering, hungry ghost, laughing madly at their confusion and horror and despair. Zuko stood slowly, half-preparing himself for some assault or treachery, Katara quivering helplessly in his arms. If they were attacked, Zuko would be their only defense; for this barren world of shadow was void of earth or ocean or sky or star, so completely black that the deepest caves in the world could not rival it. Katara leaned in closer to the inner warmth of Zuko's body, comforted by his strength, unknowingly sending a wave of cool relief over his paranoid frame.
"Zuko...where are we?" she whispered, hardly daring to breathe the words. Zuko stuttered slightly in his response, trying to focus his ears on the absolute silence around them.
"I...don't know..."
"Allow me to answer that, my friends," came the sudden, abrupt interruption from a voice so loud and powerful that it stung the ears of the two teenagers where they lay, abandoned, in the dark. Zuko whirled, having prepared himself, and called for his fire, ready to light his hands to flame; but his body did not respond to the demand, and his fists lay as cold and white and bare as they had moments before.
Confused, he looked down at his fingers, which moved as normally as ever, besides the fact that red light and heat wasn't pouring from them. Roaring, he called again for flame, passion, fury - and again his skin paled quietly as it refused.
"You'll find that quite impossible while you are here, young Prince," said the deep voice, but it held no within it there was no laughter. It was stern and old, of though the rocks of the ground itself spoke to them out of a dark and invisible earth. Katara's hand found Zuko as he swallowed, realizing his helplessness in the face of this disembodied voice, and their fingers clenched tightly.
"Who...why don't you show yourself?" said Katara fiercely. Zuko was surprised at the passion in her voice before he realized she was terrified into bravery, her hand was trembling violently in his. For a moment, there was no response, and Zuko wrapped his arm around her and she grew quite again.
"...Forgive me, my friends."
A flame ignited a few feet in front of them, casting an eerie, orange glow several feet towards them. The ground was littered with dead leaves and roots, but this was not at all what Katara and Zuko noticed. Standing before them was an old, old man, aged more deeply than the glaciers Katara had grown up climbing and the mountains Zuko had beheld in his youth. Wrinkles wore at his face like the creases of pages in an ever-lengthening book, his eyelids drooped and weary from countess, unending years. There was the semblance of a crown upon his withered brow that resembled the might of a rearing flame, his tall, straight frame wreathed in a deep crimson robe that bore similar emblems and designs. Katara had never before seen such a man, and gazed in silent astonishment; but Zuko had often seen depictions of him in his studies of the Firebenders Avatars, and he knew this one on an instant.
"Avatar Roku," he whispered.
Roku closed his eyes solemnly, as though Zuko had said something very sad that deserved a moment's silence. Katara, utterly bewildered, turned her gaze from Zuko, who's mouth hung part-ways open, and Roku, who had opened his eyes again to the light of the dancing flame.
"Yes, dear son, I was Avatar Roku," he acknowledged, half-heartedly it seemed from his tone.
"But I am now merely the Spirit of that great man; and I can aid you only with wisdom in this dark hour. Listen well, for the doom of the world hangs upon you, and there is no time to waste."
He strode forth towards them, passing directly through the fire and showing no signs of burning or singing, neither on himself nor his clothes. Katara released Zuko's hand, both of them stunned into silence by the ancient power of this long-dead Avatar, and Roku stopped before them with the light of the fire glistening at his sides. He turned first to Zuko, who stood with his knees shaking slightly, awed by the Avatar's authority which far surpassed any mortal claim. But when Roku bowed his head to the Prince, he became even more confused.
"Prince Zuko, of the Fire Nation," said Roku deeply, his voice rumbling with a great and terrifying passion. "When you depart from this place, you will carry with you, for a short time, the powers of the Sun Spirit, who's name was once Kagu. You will use this power only to resist the evil and anger that now infects the young Avatar, who alone of all the other Avatar's to walk the green earth has discovered the Hidden Darkness. You will call him, fighting away this dark shadow, and bring him back to the light with the fires of the sun."
He stretched out his finger and touched Zuko's forehead very gently, as though he blessed the Prince. But a red flash went flying from the tip of his finger and suddenly Zuko's insides erupted into a torturous, maddened hell of unbearable heat and flame, ripping viciously though his weak and untamed body, consuming him, the raw might of the sun roaring unbound and unrestrained within the limited confines of his soul - and then it faded, obedient, to the structure of his body, seeping into his veins and pumping there like hot lava ready to spill, raging and furious, at the first command of Zuko's. When Zuko first felt the immortal power he cried out, even in the face of the ever-calm Roku, and fell blindly to his knees, and Katara reached out to him; but Roku caught her eye and held her, motionless, in his gaze.
"To you, Master Katara, of the Southern Water Tribe," he whispered, his voice changed now to a low ringing that resembled the distant roll of waves. "When you, too, have left the Spirit World, you will bear with you, for awhile, the might of the Ocean Spirit, of La, of the raging waters. You will use this gift to calm the storm of anger and hatred that consumes the young Avatar, the forsaken boy who can no longer remember the wonders of love and joy. You will tend to him, soothing away his terrible pain, and quench all his deep rage with the healing waters of the ocean."
He repeated the gesture he had performed on Zuko and placed a cold finger on Katara's forehead. A fierce, bright stream of blue shot forth and vanished, and Katara felt a furious, ever-flowing fountain burst within her. The calm and serenity of water was forgotten; it rent her from ever direction, rampaging madly through her veins, threatening to burst painfully from every inch of her agonized body. It stormed through her like the hooves of a thousand bulls, goring her with their cruel horns, ripping her apart from every angle with brutish, savage strength and ferocity - and then it calmed, falling gentle like the waves beneath the eye of a storm, releasing its rage and unkept temper and glittering readily at the end of her graceful fingers.
Roku had not faltered or paused as the two received these sudden and powerful gifts; undaunted, he grabbed them each by one shoulder and forced them to look up into his face. But even as he spoke he began to fade, as though Zuko and Katara were awakening from some odd and wonderful dream.
"Listen well, and do not be wholly distracted with the wonder of these powers. If you linger, or wait, or falter in your judgement, then the world will be cast under shadow. The sun and moon will not shine again until you have brought back the true Avatar and restored the balance. For even as the Avatar is linked to the Spirit World, so the Spirits are linked to him; and by turning to darkness, the balance between both worlds is destroyed. If he remains lost in his hate and anger, all the world will whither, and the Spirits themselves perish. The world exists on Yin and Yang, love and hate, darkness and light, good and evil. You were chosen because you knew this balance within your hearts; the balance of fire and water, of passion and peace, of anger and serenity. You are now the only lights the world has, and because you are not true Spirits, the power of the Avatar will not affect you as greatly. Go quickly, and turn the Avatar back to the path of love and peace."
Then he vanished, and the darkness wavered and dispersed as though the sun was rising in one swift, fluid movement; and Katara and Zuko were left to stare into the cold, hateful eyes of Aang, the Avatar fallen to darkness.