Prologue: Sacrifice
Everything hurt.
His left eye was swollen shut. The false and last two ribs on his left side were broken. One of them was digging right into his abdominal wall. His organs were bruised, some even ruptured.
Damn it all.
He spared a brief thought for the four young charges under his care that night. It had been their first - and likely last - mission together.
Tanjiro Kamado.
Nezuko Kamado.
Inosuke Hashibira.
Zenitsu Agatsuma.
None of them would die today. He would make sure of that.
Deep breaths kept the pain of his injuries at bay. He ignored the blood splattered over the left side of his face and sheathed his sword and impaled it into the earth.
"Oh? Are you accepting my offer, Naruto?" Akaza asked with far too much hope.
"Ha!" The laugh hurt but it was worth the look of disappointment on the Upper Moon's face. "Like hell I will."
He couldn't decapitate the bastard. There was no way in hell he could do it. Cutting through the demon's arms alone had taken ludicrous amounts of strength. He didn't have much left to spare unless he went all out, and even that didn't guarantee a decapitation. The bastard would probably just move out of the way at the last second and let the sword tear through his arms or chest.
Luckily for him, there was more than one way to kill a demon.
"Don't be like that, Naruto! Join me! Become a demon! Together, we can fight and grow stronger together forever!"
He said nothing. Taking a deep breath, he altered his breathing.
"If you couldn't kill me without your sword, what do you think your fists are going to do?! Don't be foolish, Naruto! Accept my offer!"
He glanced back towards his charges. Tanjiro was on the verge of pushing himself to his feet, if only to aid him in any way he could. To that, he gave them a blinding smile.
"Everything's going to be fine, you two. I won't let you die tonight."
In that same moment, he took note of the stars, disappearing as the sky grew lighter.
Good.
"Oi, Akaza. Do you think humans are weak?"
"Uhn!" The demon grunted, that ever present smile drawing at his growing wider. "You're frail. You're mortal. And if there's anything I hate, it's weakness!"
Naruto smiled.
"Then let me show you true strength."
An aura of flames erupted from his battered body. The grinding of his broken ribs was pushed away by a growing warmth. The pain of his ruptured organs receded as his mind sharpened and focused. Nine tails of flames erupt from his back, burning as bright as the midday sun.
"Flame Breathing: Esoteric Art."
A second wave poured forth. Fire coated his arms, spread from the tips of his fingers down to his elbows. Two flame-like marks grew from his hairline down to his eyebrows as another grew spread across the right side of his jaw.
"Ninth Form: Maelstrom."
Akaza brought his arms up, ready to activate . A blazing fist slammed into his jaw regardless. Motes of fire burned away at his flesh.
"Such speed! I can barely sense him anymore!"
He barely had the time to right himself and slap away another punch, aimed for his solar plexus. Naruto pivoted on the balls of his foot, dropping his heel down from above. The demon crossed his arms, stopping the attack as his feet caved through the stone below.
"Such strength, Naruto! We both know-"
His eyes bulged as Naruto pushed himself off the demon's arms, performing another heel drop and piledriving Akaza into what would be his tomb. At that moment, the Upper Moon realized the demon slayer's plans.
"The sun!"
A flurry of blows from Naruto stopped him from freeing his legs. He reacted to many, blocking them with ease yet others, seemingly undetected, slipped through his guard. The flames licked away at his wounds and stopped him from regenerating, even if it were only for a few moments. Shattered bones and pulverized muscle that would've healed faster than the eye could see were slowed down to a comparative crawl. Still a mere second, but that was time he couldn't afford to waste.
"I have to get out of here!"
A flex of his calves shattered the stone prison he had been trapped in. He kicked Naruto, putting some distance between them, using the movement to backflip away from the blond. Just as he turned to run into the forest and its protective shade, he gave a look back towards the rising sun. What he saw struck fear into his demon heart. Naruto, who had been over twenty meters away, was nearly on top of him, his right arm reared back.
"Yes! Punch me! Get me away from the-!"
The blond muttered something, though he was moving far too fast for the sound to reach him, yet he could read the man's lips all the same.
"Kagutsuchi."
The Hashira's fist unclenched hand straightening into a knife hand. A cone of fire enveloped the extended digits. Even from afar, Akaza could feel the scorching heat as it seared away the flesh of his back, a pain he likened to the sun's immolating light.
Out of desperation, he fought back. His fist came up, aimed squarely for the Hashira's chest. It was an attack the demon slayer could have dodged with his eyes closed, but it would have forced him to abandon the attack.
Their eyes met. For a brief moment, Akaza realized why he had been so adamant on having Naruto become a demon.
He reminded Akaza of himself; he could see it in those now flaming golden eyes. The strength. The resolve.
Skin. Muscle. Bone. Organs. Nothing stood in the way of his fist, Akaza noted. The Hashira's momentum had carried him forward; flesh could not survive against two unstoppable forces. At the same time, Naruto's arm pierced straight through his left pectoral, straight through his heart and out of his back. It was a wound he could regenerate in a split second.
But not with the arm still in his chest.
"YOU IDIOT!" he screamed. "LET GO!"
He aimed a punch squarely for the demon slayer's head, intending to take it off in a single swing. A fiery palm caught onto his forearm, fingers digging into the flesh as he stopped the punch mere centimeters away from his cheek. The flames around Naruto only continued to burn, scorching away flesh and muscle until only a mess of bubbling tissue remained. Blue skin and red muscle regenerated right over the injuries…
… on top of the fingers wrapped around the radius and ulna bones.
"NO NO NO!"
The two moved about one another, trying to force each other to concede through their footwork.
"Heh." A cough splattered blood against Akaza's face. "Who's weak now, asshole?"
