The Infinity Castle groaned, its walls bending and twisting like the ribs of a living monster. The battlefield was a storm of clashing wills—each corner ignited by battles that would decide the fate of humanity.
Murata's blade still shimmered with the newborn cosmos, Galaxy Breathing burning with defiance against Kokushibo's infinite moons. Every arc of their clash ripped apart reality, stars shattering against crescent blades.
Tanjiro sprinted across the crumbling floor, Nichirin blade blazing in his hand. His lungs ached, but his determination burned hotter than the fire on his sword. He skidded to Murata's side, eyes fierce.
"Murata-san! You're not alone!"
Murata, sweat and blood dripping from his jaw, gave a quick grin despite the void's crushing weight pressing down on him. "Then let's cut through this night together, Tanjiro!"
Kokushibo's six eyes narrowed, focusing on them both. His voice was a low growl. "Pathetic. Even with two blades, you think you can reach me? You are dust beneath the moons."
Tanjiro exhaled—Hinokami Kagura: Burning Bones, Summer Sun!—his flame wheel crossing Murata's stellar arc. Their combined strike split Kokushibo's crescent, forcing the Upper Moon One to actually step back. For the first time in centuries, Kokushibo's lips curved into something close to respect.
"This might be… entertaining."
Elsewhere, Shinobu's lungs burned with the icy frost spreading from Dōma's every movement. Her strikes landed, her poisons seeping, but his regeneration was monstrous. He twirled his fans, spewing shards of ice across the battlefield, turning everything into a frozen hell.
Then came a roar.
Inosuke dove in, dual blades flashing. His beastlike fury carved through the frost, shattering ice lotuses in a storm of jagged steel. He landed beside Shinobu, chest heaving.
"That bastard killed my mother!" His voice cracked like a wounded animal, rage and grief bleeding together. "He won't live another second while I breathe!"
Shinobu's eyes widened briefly, then softened with grim understanding. "Then we fight together. My poison… your fangs."
Dōma tilted his head, mock sympathy dripping from his smile. "Ahh… so you're that child. Yes, yes, I remember now. How quaint. Do you think this reunion will change the outcome?"
Inosuke snarled, charging with animalistic fury. Shinobu darted in with him, their combined fury slicing through Dōma's blizzard.
On another tier, Nezuko's eyes glowed with burning resolve as demons swarmed endlessly from the walls and floors. Her body burned with remnants of the sun's touch, but instead of crippling her, it strengthened her blood techniques beyond limit.
"Blood Demon Art: Exploding Blood!"
Flames erupted in every direction, purging dozens of demons at once. She fought like a whirlwind of fire and claws, clearing entire waves, her presence a beacon of salvation amidst the chaos.
Each scream of the lesser demons was drowned beneath her fiery rage, her movements feral but filled with a fierce, protective love.
And then, lightning split the battlefield.
Zenitsu froze, his golden eyes trembling as he saw the figure standing across from him. A mocking grin stretched across Kaigaku's face, crackling with dark, corrupted thunder.
"Zenitsu… pathetic little coward. Look at you—still shaking. Our master chose wrong. I became a demon, and he chose to end himself rather than accept me. His blood is on your hands as much as mine."
Zenitsu's throat tightened, his heart ripping apart. Master Jigoro's kind smile flashed in his memory, the weight of his sacrifice pressing down like a blade. His fists trembled.
"…you…" Zenitsu's voice cracked, lightning sparking along his sheathed blade. "…you're the reason he died."
Kaigaku sneered, drawing in dark electricity that split the floor around him. "Then prove you're more than a failure. Show me the strength he saw in you before I rip it apart!"
Zenitsu's eyes hardened. His breathing slowed, the fear burning away into raw, unwavering focus. His hand gripped the hilt, lightning crawling along his arms.
"For Master… for everyone… I'll strike you down!"
The two thunder-breathing disciples launched forward, lightning devouring the void.
Lightning split the Infinity Castle, jagged bolts tearing across the warped sky as two figures stood opposed. The air itself was alive with static, each breath sharp and burning in their lungs.
Zenitsu's legs trembled—not from fear, but from the electric current racing through him, pooling in his veins. Across from him, Kaigaku sneered, his eyes glowing with malice, his blade wrapped in dark, corrupted thunder.
"Still shaking, Zenitsu. You always were pathetic." Kaigaku's laugh echoed, cold and venomous. "Master wasted his time on you. I was always stronger. Always faster. And now—" his aura flared, black lightning ripping the floor beneath his feet "—I'm immortal. I surpassed you long ago."
Zenitsu's heart clenched at the mention of their master. He saw Jigoro's wrinkled smile, the warmth in his eyes, the steady hand that once rested on his shoulder when he was a boy too scared to even draw his sword. And then he saw the stillness of his corpse, the blood pooling around his body—an honorable death for a man who couldn't accept Kaigaku's betrayal.
Zenitsu's teeth ground together. His fear was still there, but it no longer ruled him. It became fuel, crackling like the storm within.
"You…" Zenitsu's grip tightened on his hilt. His eyes lifted, clear and blazing for the first time. "You don't get to speak his name."
Kaigaku snarled. "Shut your mouth!" He vanished in a burst of black lightning, blade swinging down like judgment itself.
Zenitsu moved too. Thunder Breathing, First Form: Thunderclap and Flash.
Their swords clashed in a blinding collision, thunder and black fire splitting the air. The floor beneath them fractured, cracks racing like spiderwebs across the castle's warped surface.
Kaigaku's strikes came in relentless waves, corrupted thunder exploding with each slash. Zenitsu was forced back, sparks flying from his blade as their swords clashed faster than the eye could follow.
"Face it!" Kaigaku roared, his attacks vicious, wild. "You'll never beat me! You were always the coward hiding behind others while I did the work. You survived because Master coddled you!"
Zenitsu slid back, chest heaving, then shut his eyes. His breathing slowed, his focus narrowing. The fear faded. Only one truth remained—the vow he made before his master's grave.
I will never run again.
His feet dug in, his body becoming one with the storm.
Kaigaku leapt high, black lightning curling into the shape of a dragon around his sword. "Die, Zenitsu!"
Zenitsu's eyes snapped open—gold blazing. His blade hummed, a roar of pure thunder echoing through the chamber.
"Thunder Breathing, Seventh Form: Honoikazuchi no Kami!"
A colossal dragon of pure golden lightning erupted from his strike, meeting Kaigaku's corrupted storm head-on. The two beasts clashed midair, the explosion tearing apart the chamber, light and sound consuming everything.
Kaigaku screamed as Zenitsu's lightning devoured his. The golden dragon surged forward, wrapping him in blinding radiance. His body convulsed, torn apart by the purity of Zenitsu's storm.
"No! I was stronger! I was—!"
The rest was lost to thunder.
When the light finally faded, Zenitsu stood panting, blade still raised, the storm flickering out around him. Kaigaku lay broken on the ground, smoke rising from his charred form, his corrupted lightning extinguished forever.
Zenitsu's knees buckled, but he steadied himself, tears sliding silently down his cheeks. He whispered into the silence, voice trembling yet proud.
"Master… I kept my promise."