The wind swept through the old training grounds of Arctis, carrying with it the scent of iron and wet earth. The sun hung low, bleeding gold light across the scarred wooden posts that had once marked the path of young warriors. Laughter echoed faintly — the sound of boys who hadn't yet learned what war really meant.
Kaien Draven stood in the center of the field, his hands wrapped around a dull practice blade. Sweat ran down his neck, and his breath came out ragged, but his eyes still burned with determination. Across from him stood Ethan Vale, tall, steady, and calm as ever. His own practice spear rested lightly against his shoulder.
"You swing like you're angry at the world again," Ethan said with a grin. "Relax your grip. Anger makes your blade heavier."
Kaien scowled. "Tell that to the demons that burned my home."
Ethan sighed and planted his spear into the dirt. "You keep fighting ghosts, Kaien. If you carry that much hate, one day it's going to eat you alive."
Kaien glared at him but said nothing. He swung again, faster this time, the blade cutting through the air with a sharp hiss. Ethan watched him for a moment before suddenly moving — a blur of motion — and with a quick flick, disarmed Kaien in one smooth strike. The sword spun into the dirt.
Kaien stared at him, breathing hard. "You cheated."
"I didn't," Ethan said calmly. "You hesitated. That's worse."
For a second, Kaien's pride flared, but then his shoulders loosened. He bent down, picked up his sword, and let out a breath. "You always do that."
Ethan smiled. "That's why you keep me around."
They trained until the sun began to fade behind the hills, the air cooling as the sky turned to crimson. When they finally sat on the fence overlooking the valley, the lights of the city below were just starting to glow — hundreds of flickering lanterns painting gold trails across the mist.
"Do you ever wonder," Kaien said quietly, "if we're fighting a war we can't win?"
Ethan tilted his head. "Against the demons?"
Kaien nodded. "The world's been at war for centuries. Every time we kill one, another takes its place. Maybe we're just feeding the fire."
Ethan leaned back, staring at the horizon. "Maybe. But we fight anyway. Not because we'll win. Because people behind us deserve a chance to live without fear."
Kaien looked at him. "You really believe that?"
Ethan smiled faintly. "If I didn't, I'd be just like them."
The silence stretched between them — not heavy, but thoughtful. Kaien looked down at his calloused hands, the same hands that would one day carry the weight of countless lives. "You're too good for this world, Ethan."
"And you," Ethan said, clapping him on the shoulder, "care too much about pretending you're not."
They laughed — a sound that would later haunt Kaien like a ghost.
Time passed, and the years hardened them both. The boys became soldiers. They rose through the ranks together, side by side, until their names became legend among the Vanguard. Kaien, the blade that never broke. Ethan, the light that never dimmed.
Then came the day of the Red Horizon — the battle that changed everything.
The world was fire.
Demons poured from the rift like a flood of nightmares. The Vanguard army shattered under the onslaught, their formations broken, their leaders dead or fleeing. Kaien and Ethan fought shoulder to shoulder, their blades cutting through the endless swarm.
Kaien's voice rose above the roar of battle. "We can't hold this line forever!"
Ethan stabbed a demon through the throat and spun. "We just have to hold until the civilians escape!"
The ground cracked beneath their feet. A massive demon general emerged — ten feet tall, skin made of molten obsidian, its roar shaking the mountains. Kaien raised his sword, eyes blazing. "Go! I'll—"
"No," Ethan said firmly, stepping beside him. "We end this together."
They charged.
The world became chaos — light against shadow, fire against flame. Kaien's sword tore through the creature's armor, while Ethan's spear blazed with radiant energy, each strike burning through the darkness. But the demon was too strong. With one massive swing, it sent Kaien flying into the ruins.
"Kaien!" Ethan shouted, diving toward him.
Kaien groaned, blood dripping down his face. "Don't— you'll die!"
The demon turned its gaze toward Ethan, its claws glowing with dark fire. In that split second, Kaien saw it — the flash of movement, the inevitable end.
Ethan looked back at him and smiled.
"Guess I'll have to prove I'm better than you one last time."
He raised his spear, channeling every drop of his life force. A surge of white light exploded around him, brighter than the sun. The air cracked, and time itself seemed to stop. Kaien screamed his name, but Ethan was already gone — his body consumed by the radiance.
The explosion vaporized the demon, the blast tearing through the battlefield. When the light faded, Ethan lay still at the center, the spear broken beside him.
Kaien crawled toward him, his hands trembling. "No… no, don't you dare."
Ethan's eyes fluttered open weakly. "You see, Kaien… I told you not to fight angry. Fight for something worth living for."
"Stay with me," Kaien choked out. "We're not done yet."
Ethan smiled faintly, his voice fading. "Then finish what we started."
And then — nothing.
The battlefield went silent except for the crackling of distant fires. Kaien sat there for a long time, holding what was left of his brother, the light dimming in his arms. When dawn came, only the shadow of his grief remained.
From that day, the world began calling him the Demon Slayer — not because he destroyed demons, but because he had nothing left to lose.
---
Years later, Kaien would still hear Ethan's voice — soft, distant, echoing in moments when he was about to fall. And though the darkness inside him grew, a single spark remained — the memory of a friend who believed he could still be more than his rage.
That spark became the only light strong enough to face the abyss.
And that was how the legend of the Demon Slayer was truly born.