Symbiosis
A/N: Um, basically spoiler for anything before ch 433 of the Manga. Character death . . . sorry, I just can't see it any other way.
A chill wind swept across the field, patches of green grass bending under the oppressing gusts, the rest already weighed down by patches of red splatter. Despite the fresh air, nothing could disguise the iron stench wafting through the breeze. It permeated the ground, the sky, the past and the future. It dripped from Sasuke's chokutō, a never-ending flow of crimson that wept for all those whom he had killed and all the sins that he had committed – the greatest of which would forever condemn him to the 9th circle; the greatest of which was against the man before him.
Sasuke watched Naruto stand a bit out of breath, the wind whipping the gold and red strands against his face. Though the sounds of battle had been deafening not more than a sunrise ago, it was now eerily silent. All that reached his ears was the wind carrying the Furies upon its back, fueled by Orochimaru, by Itachi, by all the Konoha shinobi he'd already dispatched. But looking into those pure, blue eyes, the cry of the Furies faded into the background. Suddenly, Sasuke was 7 again and turning from the sun's reflection upon the lake to see another sun walking along the dock. The sun smiled down upon him and he was instantly mesmerized by the twin blue patches of sky peeking from between the rays.
"So the bastard's finally decided to come home." Unceremoniously snapped from his memories, Sasuke steeled his eyes and tightened the hold upon his sword. The blond continued, "How could you Sasuke? You've destroyed almost everything I've ever loved. I've worked so hard, all these years, so that I could bring you home. And now, now . . . Now that you're finally back, I'll have to . . . kill you before you complete your destruction of my, no, our village." Sasuke narrowed his gaze. The dobe would never understand. Revenge was simply not a part of Naruto 's consciousness. His was too filled with . . . goodness . . . something that Sasuke had always envied.
Naruto had paused, with an expectant look upon his face. Maybe he expected an apology, a rebuttal, anything to prevent the inevitable that he regretted even before it had started. Sasuke, knowing that there was nothing he could say to convey the remorse and pain he'd been towing since he'd abandoned Naruto those many years ago, pressed his lips together into a thin line as two black and red atomic orbitals replaced his pupils and chidori energized his chokutō.
"Kage Bunshin no Jutsu!" Two Naruto clones popped up. Without warning, the last battle had begun. Sasuke could feel the intense chakra that was now accumulating on one of the Narutos' hand. Soon, red started bleeding into the blue ball of air, the energy so strong that Sasuke felt like he'd be swallowed. With a hollered "Fūton: Rasen Shuriken!" Naruto released the ball of energy and it hurtled toward Sasuke at an amazing speed. Having no time to jump away, even with his Mangekyo Sharingan slowing down the action, the only thing he could do was bring his charged chokutō in front of him and putting every ounce of chakra he could manage into the sword.
A loud boom cut through the sound of 10,000 birds. As intense energy pressed down all around him, Sasuke could feel the ripples of the boom like hammers pounding through the pores of his skin. Time passed, stopped, rewound; he lived and died ten lives. Suddenly, everything was gone again and he felt the air waft gently around him. The contrast between such gentleness and the hammering stung his senses. He realized he was hunched over the ground, knees bent below him and a bright red stream of blood dripping from his nose. His chokutō had broken in two, the half with the handle fallen on the ground near his clenched hands and the other out of sight. Using the broken sword as a crutch, Sasuke slowly rose to his feet and looked straight ahead.
A red glow had surrounded Naruto and three tails flamed up behind him. He was panting heavily from the amount of energy he'd put into his attack; he looked so weary, though probably not nearly as tattered as Sasuke, who'd used half his life to split that Rasen Shuriken. By pure miracle, he still had enough energy left for Amaterasu. Quickly, before Naruto could produce his next attack, Sasuke sent the black flame forward. In an instant, it had engulfed Naruto, who howled with agony. The sound was so deep that it reverberated through the earth beneath Sasuke's feet and into his shattering heart. Just as despair overtook Sasuke, the flames suddenly disappeared as if sucked into Naruto's chest.
He was still numb with surprise when Naruto dug a Rasengan into his chest. Instantly, he lost his breath. It felt so odd that it was over so quickly; especially since it seemed he'd anticipated this moment all this life. As he felt his back hit the ground, Sasuke looked up into those crystal blue eyes and felt droplets hit and slide down his face. As the streams reached his lips, he could taste the salt mixed with anguish. Naruto's face came closer and suddenly, Sasuke felt his breath come back. As Naruto's lips melded with his own, life had decided to come back to him for this last moment. The kiss was passionate and gentle, angry and sad, bold and shy, but all of it regretful.
When Naruto pulled back, Sasuke let out a long sigh, his life expelling from his body. Watching the upward curve of Sasuke's lips, all Naruto could do was cradle the head in his lap and let out the wail of someone betrayed by life. After all, it's not every day that you kill the only person you've ever loved.
As an explanation: the reason the Amaterasu didn't work on Naruto in this story is because immunity to it was what Itachi gave Naruto that one time they met in the woods. I have no idea what Itachi actually gives Naruto, but I hope we find out soon!