The wind carried ash instead of snow. The mountains of Argrath were alive with fire—rivers of molten stone flowing through the cracks of ancient cliffs. Kaien Draven stood at the base of the infernal range, his cloak whipping behind him, the mark on his chest faintly glowing through his armor.
He had been walking for three days straight without rest. The path was unforgiving, every step echoing with the growl of the earth itself. The Sanctuary of the First Flame was said to lie somewhere within this cursed labyrinth—a place where the light of creation and destruction met in eternal balance.
To Kaien, that balance was slipping further away each day.
The corruption inside him was growing. He could feel it now—not just as whispers or pain—but as a pulse that matched his heartbeat. The abyss was alive inside him, and its hunger was endless.
Still, he pressed on.
By the time he reached the entrance of the Flame Chasm, the air was scorching. The stone archway before him shimmered with inscriptions in an ancient tongue—runes older than the gods themselves. Kaien traced them with his fingers, and the symbols lit up in a spiral of gold and crimson.
"Light and shadow intertwined," he murmured. "So this is it."
He stepped through.
The air changed instantly. Inside, the chasm was vast and glowing—a cathedral of living fire. Massive pillars of obsidian rose from molten rivers below, and bridges of hardened flame stretched across the abyss. The heat was unbearable, but Kaien's corrupted aura protected him just enough to keep walking.
At the center of the chamber stood a circular platform engraved with the sigil of the First Flame. Its light pulsed like a heartbeat. Kaien approached slowly, the ground trembling beneath his boots.
Then he heard it—footsteps.
He turned sharply, hand on his sword. Out of the swirling smoke, a figure emerged—a man cloaked in crimson armor, his face hidden beneath a helm shaped like a demon's skull. His presence alone warped the air, and Kaien felt the familiar sting of dark energy radiating from him.
"So," the man said, his voice deep and smooth. "You made it here after all."
Kaien's eyes narrowed. "Who are you?"
The stranger stepped closer, the firelight glinting off his armor. "Once, I was like you. A Slayer. A guardian of the Flame. Until I learned the truth."
Kaien raised Noxveil slightly. "What truth?"
"That light and darkness are not enemies—they are halves of the same being. And to deny one is to destroy both."
Kaien frowned. "You sound like the kind of man who fell too far to climb back."
The figure chuckled. "Perhaps. But I climbed higher than any mortal before I fell." He reached up, removing his helm.
Kaien froze.
The man's face was scarred but unmistakable—his eyes burned with the same red glow Kaien saw in his own reflection. His hair was white as ash.
"I don't understand," Kaien said. "You're—"
"Eryndor Draven," the man said with a faint smile. "Your father."
The words struck Kaien like a blade through the chest. "That's impossible. My father died during the Purge War."
"Is that what they told you?" Eryndor asked softly. "That I fell in battle? No, Kaien. I was sealed away here—guarding the First Flame from those who would destroy it. Until the day I chose to merge with it."
Kaien's grip on his sword tightened. "You merged with the Flame? That's suicide."
Eryndor's expression darkened. "It was transcendence. I saw beyond the veil of life and death, of light and shadow. And I saw what you are destined to become."
"I don't want your destiny," Kaien growled.
"But it's already inside you," Eryndor said. "That mark on your chest—the power you've been cursing—it's my legacy."
Kaien took a step back, disbelief twisting his voice. "You're the one who cursed me?"
"Not a curse," Eryndor said quietly. "A safeguard. When you were born, I felt the abyss stirring again. I sealed part of my own power inside you—to give you the strength to stand against it."
Kaien shook his head. "You turned me into a weapon."
Eryndor didn't deny it. "You were never meant to be human, Kaien. You were meant to be balance itself. The bridge between creation and ruin."
The words echoed in Kaien's mind like thunder. He remembered every moment of his life that felt out of place—every time he healed too fast, every time his aura cracked the air, every time people looked at him not with pride, but fear.
All of it made sense now.
"I didn't ask for this," Kaien whispered.
"No one ever does," Eryndor said softly. "But you can't run from it. The world is crumbling because both sides—light and darkness—refuse to coexist. The Demon King seeks to consume everything. The Celestial Order seeks to purge everything. Only one who bears both can restore the balance."
Kaien looked at him sharply. "You want me to side with you?"
"I want you to awaken," Eryndor replied. "To understand that you are not fighting against the darkness—you are its master."
Kaien's aura flared, the ground cracking beneath his feet. "No. I'll never be like you."
Eryndor's eyes glimmered faintly. "You already are."
He raised his hand, and the air exploded with light and flame. Kaien barely managed to dodge as a pillar of fire erupted where he stood. His sword came up instinctively, clashing with his father's flaming blade. The collision sent ripples of heat through the chamber.
"You've grown strong," Eryndor said, forcing Kaien back. "But you're still bound by fear."
Kaien shouted, pushing forward. "I'm bound by choice!"
The two blades clashed again and again, each strike a storm of fire and shadow. Sparks flew like meteors as they fought across the burning bridges. Kaien's movements were wild but precise—every swing driven by emotion, every block powered by defiance.
Eryndor fought with calm brutality, each motion controlled, efficient. His blade was a river of flame; Kaien's, a thunderstorm of darkness. Together, they painted the battlefield in chaos.
At one point, Kaien broke through his father's guard and struck, slicing across his chest. Eryndor didn't even flinch. Instead, he caught Kaien's arm and threw him backward into a wall of molten stone.
"You can't win this fight," he said.
Kaien rose slowly, his breathing heavy, his armor cracked. "I don't need to win. I just need to prove you wrong."
His eyes blazed crimson. The mark on his chest spread, veins of black lightning crawling up his neck. His sword pulsed violently.
Eryndor's gaze softened. "Then show me what you've become, my son."
Kaien roared, unleashing everything.
The chamber erupted. Shadowfire poured from his blade, mixing with the flames of the chasm. The explosion shook the mountain to its roots. For a moment, light and darkness became one—a storm of colorless power that burned the air itself.
When it cleared, Kaien was on his knees, his sword buried in the stone. Eryndor stood over him, his armor cracked, smoke rising from his wounds.
He knelt down and placed a hand on Kaien's shoulder. "You've surpassed me."
Kaien looked up, dazed. "What…?"
"You've done what I couldn't," Eryndor said, smiling faintly. "You fought both halves of yourself and didn't lose either. You found balance."
Light began to pour from his body. Cracks of fire spread across his armor.
"Wait—what are you doing?" Kaien shouted.
Eryndor's voice was calm. "My time ended long ago. But my strength doesn't have to."
"No!" Kaien tried to pull away, but Eryndor's light wrapped around him, flooding into his chest. The mark burned white-hot, then dimmed.
"Remember this, Kaien," Eryndor whispered as his form began to dissolve into light. "The flame is not your enemy. It is your heart."
And then, he was gone.
The chamber grew silent. The flames softened. The sigil beneath Kaien's feet glowed brighter than ever before.
Kaien knelt there, shaking, his mind spinning. The ache in his chest was gone. The corruption's voice had vanished.
He stood slowly and looked around. The Sanctuary pulsed with steady light now, no longer wild or unstable.
Kaien lifted his sword, watching as it shimmered with both black and white light. Two halves, finally united.
He whispered softly, "Father… thank you."
The mountain rumbled in response, as if answering him.
Kaien turned and began the long walk back toward the surface. His steps were slow but sure. For the first time in years, his mind was quiet.
When he emerged at the mountain's peak, dawn had broken. The first light of the new sun spread across the scorched horizon, painting the world in gold and crimson.
Lira stood there waiting, her cloak whipping in the cold wind. When she saw him, her eyes widened.
"You're alive."
Kaien smiled faintly. "Barely."
She walked closer, studying his face. "Something's different about you."
He nodded. "I found what I was looking for."
"And what was that?"
Kaien looked out toward the horizon. "Balance."
She followed his gaze, her expression softening. "Then maybe… there's still hope for this world after all."
He glanced at her. "Hope's fragile. But it burns bright if you protect it."
They stood there together as the sun rose higher, casting long shadows over the world that was still healing from war. The flame in Kaien's chest pulsed once—steady, alive, and calm.
And somewhere deep in the abyss, far beyond the mortal realm, the Demon King stirred. His voice rumbled like thunder in the void.
"So, the heir of balance has awakened. Then the true war begins."
Kaien's gaze hardened as if he had heard it himself.
"Let it come," he said quietly. "This time, I'm ready."
The wind roared. The world held its breath.
And the path of the Demon Slayer burned anew.