The transformed blade caught the moonlight like shattered glass—each auxiliary edge a crescent fragment that seemed to exist in multiple places at once. Kokushibo's six eyes reflected the pale glow as he settled into his stance, the grotesque weapon humming with anticipation.
Behind Akira, the group stood frozen in the wake of power that made the air itself feel heavy.
"We have to do something," Tanjiro whispered, his hand instinctively moving toward his sword. His voice cracked with the weight of helplessness. "We can't just stand here while Akira-san fights alone."
"And what exactly would we do?" Yushiro's response came sharp, but his hands trembled. "Did you see how they moved? I couldn't even track them with my Blood Demon Art." He clenched his fists until his knuckles went white. "We'd be slaughtered before we took three steps."
Nezuko pressed closer to her brother, her eyes wide as she watched the two figures facing each other in the clearing. A soft sound escaped her throat—something between fear and frustration.
Tamayo's gaze remained fixed on Akira's back, her centuries of experience reading the subtle language of combat. She saw the controlled breathing, the perfect distribution of weight, the way his fingers adjusted minutely on his sword grip. Details that spoke of mastery earned through countless hours of practice. "Even if we wanted to help..." she began slowly, "we would only become liabilities."
"But Lady Tamayo—" Yushiro started.
"Look at him, Yushiro." Tamayo's voice carried a strange mixture of sadness and certainty. "Truly look. That stance, that focus—he's not fighting for survival. He's fighting to win."
Tanjiro's jaw tightened. The Demon Slayer Mark on his face throbbed with his racing heartbeat. "There has to be something. We can't just—"
"You saw what happened when their blades first met." Tamayo turned to face them, her expression grave. "The shockwave alone destroyed the trees around them. If we enter that space..." She didn't need to finish the sentence.
"So we just watch?" The words tore from Yushiro's throat, raw with impotent rage. "We just stand here while he risks his life?"
Tamayo's hand found his shoulder, gentle but firm. "We trust him. And we stay alive. If Akira-san dies fighting Kokushibo, our chances against Muzan die with him." Her fingers tightened. "But if we die trying to help, we guarantee his failure. We become the reason he loses focus, the opening that gets him killed."
The truth of her words settled over them like a physical weight.
Tanjiro's hand fell away from his sword, though every instinct screamed at him to move, to act, to do something other than stand helpless. "This feels wrong," he whispered.
"It is wrong," Tamayo agreed quietly, her eyes returning to the clearing. "But it's also our only option."
Nezuko made another sound, softer this time. Her hand found Tanjiro's, squeezing with all the reassurance she could offer without words.
"Lady Tamayo," Yushiro's voice emerged hoarse. "Do you really think he can win?"
The former physician watched Akira adjust his stance, watched the way his crimson blade caught the light, watched the absolute stillness that preceded violence. "I've lived for over four hundred years," she said softly. "I've seen countless warriors face demons. Most died. Some survived. But Akira-san..." A strange light entered her eyes. "He reminds me of someone. Someone who refused to accept limits, who made the impossible look effortless."
She paused, memory flickering across her features—a young swordsman with a kind smile and devastating skill, centuries dead but never forgotten.
"Yes," Tamayo said finally. "I believe he can win."
---
In the clearing, two predators studied each other across fifty feet of torn earth.
"Your transformation is impressive," Akira said, his voice carrying easily through the unnatural silence. "Most demons rely on regeneration and brute force. You've turned your body into a weapon."
Kokushibo's head tilted fractionally, the gesture eerily bird-like. "You speak as though... you have encountered many demons."
"Enough to know the difference between power and skill." Akira's grip shifted on the Divine Sword. "You have both. It's almost a shame I have to kill you."
"Your confidence..." Kokushibo's multiple eyes narrowed. "It is not bravado. You genuinely believe you can defeat me."
"I know I can."
Something flickered in those six golden orbs—not anger, but perhaps curiosity. "Four hundred years," Kokushibo said quietly. "I have perfected Moon Breathing for four centuries. I have slain countless Hashira, warriors whose names were legendary in their time." His transformed blade rose slightly. "What makes you different?"
Akira's smile was cold. "I'm not human."
"I know." Kokushibo's eyes seemed to penetrate through flesh and bone. "Your body... the cellular structure, the density of muscle fiber, the cardiovascular system—all fundamentally different. You are something else entirely."
"Then you understand why this is already over."
"No." The word carried absolute conviction. "I understand why... this will be interesting."
Kokushibo moved.
The Seventh Form erupted like a crescent moon exploding into fragments. His transformed blade carved through the air in a frontal slash that seemed simple—until dozens of curved and straight slashes materialized from nothing, expanding outward in a geometric nightmare. Each subsidiary blade carried enough force to bisect stone, and they filled the space between the two fighters like a cage of razors.
Akira's body twisted with impossible fluidity, his Viltrumite physiology allowing angles and speeds that would shatter human bones. The Divine Sword sang, deflecting three slashes in a single motion while his body slipped between four others. His feet barely touched the ground as he flowed through the killing field like water through cracks.
"Ryūshōsen!"
The attack came from Kokushibo's left side—a rising spiral slash designed to exploit the opening created by his own technique. The Divine Sword shrieked upward, carrying momentum that should have required both hands but was executed with one. The impact sent sparks cascading like fireflies.
Kokushibo's blade intercepted, but the force drove him back two steps. Before he could reset, Akira pressed forward with "Ryūtsuisen!"—descending from above like a falling star, blade aimed at the crown of his skull.
The demon pivoted, his transformed sword rising in a defensive arc. Steel met flesh-blade with a sound like a bell cracking. The ground beneath Kokushibo's feet fractured, spiderweb cracks spreading ten feet in every direction.
"Your sword..." Kokushibo's voice remained steady despite the power behind the strike. "It should not be possible. No nichirin blade possesses this quality."
"I told you," Akira said, landing in a crouch. "This is something else entirely."
"Then I will examine it... after I slay you with my blade"
The Eighth Form—Moon-Dragon Ringtail—came without warning. Kokushibo's twisted blade carved a massive, sweeping arc that stretched thirty feet, and in its wake appeared dozens of crescent moon slashes that hung in the air like frozen waves. Each one pulsed with cutting force, creating a wall of death that advanced with the inexorable patience of a tide.
Akira's eyes tracked every trajectory, his mind processing patterns faster than conscious thought. The Hiten Mitsurugi-ryū emphasized prediction—reading breath, muscle tension, the microscopic shifts that preceded every attack. His body moved before his mind finished analyzing, ducking under the first wave, twisting past the second, his blade deflecting the third with millimeter precision.
But there were too many. One grazed his shoulder, drawing a thin line of red. Another carved through his sleeve. A third would have removed his arm if he hadn't jerked back at the last instant.
"You're bleeding," Kokushibo observed. "First blood is mine."
Akira glanced at his shoulder where the cut was already closing, skin knitting together with Viltrumite efficiency. "First blood means nothing if you can't land the killing blow."
He exploded forward, closing the distance in a blur. "Sōryūsen!"
His blade became a twin-headed dragon—two simultaneous strikes from different angles, the technique exploiting the fact that even Kokushibo's six eyes couldn't track two perfectly timed attacks occupying the same moment. The first slash targeted the throat; the second, the heart.
Kokushibo's transformed sword met both, but the impact drove him backward, his feet carving furrows in the earth. Before he could recover, Akira followed with "Ryūkansen Tsumuji!"—a spinning slash that added rotational force to cutting power, the blade whistling as it carved through air.
The demon's eyes widened fractionally. He twisted, the slash missing his neck by inches and instead carving through a tree fifty feet behind him. The ancient pine toppled with a groan, its trunk sheared clean.
"Fast," Kokushibo murmured. "Faster than any human I have encountered."
"I'm just getting started."
The Ninth Form—Waning Moonswaths—erupted in Kokushibo's immediate vicinity. His blade traced multiple curved slashes in rapid succession, each one leaving crescent moon blades that overlapped and interwove, creating a defensive barrier of cutting force mere feet from his body. The technique turned him into an untouchable nexus of death, the air around him literally shredded.
Akira skidded to a halt, his forward momentum arrested by the killing field. His eyes narrowed, tracking the patterns, searching for gaps that might not exist.
"You cannot close the distance," Kokushibo stated. "This technique creates an absolute defense. Any approach results in death."
"Absolute defense?" Akira's grip shifted on his sword. "There's no such thing."
He pivoted, his body dropping into a stance so low his knee nearly touched the ground. The Divine Sword angled behind him, the position reminiscent of a coiled spring. Then he moved—not forward, but in a wide arc, circling at a speed that left afterimages.
Kokushibo's six eyes tracked him, the crescent moon barrier shifting to maintain coverage. But the constant adjustment required focus, required minute recalculations with each position change.
Kokushibo said. "You cannot—"
Akira stopped, planted his feet, and thrust forward. Not a slash, but a precise stab that threaded between two overlapping crescent blades with less than an inch of clearance on either side. The Divine Sword's point drove toward Kokushibo's heart with missile-like precision.
The demon's sword came down in a desperate parry, the impact sending both fighters skidding backward. Kokushibo's eyes—all six of them—showed surprise for the first time.
"Impossible. The gap was..."
"Seven-eighths of an inch," Akira finished. "More than enough."
Before Kokushibo could respond, the Tenth Form activated. His transformed blade began to spin, creating three massive circular saw-like slashes that rotated independently, each one sprouting crescent moon blades that followed their path. The technique filled the space between them with a storm of cutting edges that moved in unpredictable patterns, the circular slashes grinding through anything they touched.
Trees disintegrated. The earth was carved into spiraling furrows. Even the moonlight seemed to fragment, refracted through the maze of spinning death.
Akira's perception dilated. The world slowed—not literally, but in the way his Viltrumite brain processed information faster than human neurons could fire. He saw the patterns, the rhythm, the spaces between the chaos where flesh could exist for fractions of a second.
He moved.
His body flowed through the grinding storm like smoke, each step placed with absolute precision, each angle calculated to within microns. The Divine Sword deflected the slashes he couldn't avoid, the impacts sending numbing vibrations up his arm but never stopping his forward progress.
"You're trying to overwhelm me with chaos," Akira said, his voice calm despite navigating certain death. "But chaos has patterns. Everything has patterns."
He emerged from the storm three feet from Kokushibo, completely unscathed.
The demon's multiple eyes widened. "You... saw through the Tenth Form."
"Your Moon Breathing is offensive and destructive ," Akira admitted. "But it makes patterns predictable."
"Then try... this."
The Fourteenth Form—Catastrophe, Tenman Crescent Moon—detonated with Kokushibo at its center. His transformed blade moved in every direction simultaneously, creating a multitude of curved slashes that expanded outward like a nova. The crescent moon blades grew larger as they traveled, creating an omni-directional vortex that surrounded him in a sphere of cutting death that extended forty feet in all directions and kept growing.
The ground was shredded. Trees were reduced to splinters. The very air screamed as it was carved into pieces. The technique was absolute annihilation made manifest, a killing field that left nothing standing.
Akira launched himself upward, his Viltrumite physiology allowing a vertical leap that carried him thirty feet into the air. But the vortex expanded faster, the crescent blades reaching for him like grasping hands.
"Ryūsōsen!"
Mid-air, he became a blur of motion. His blade moved in every direction, creating his own storm of steel that intercepted the crescents. Sparks cascaded like a waterfall of stars. Each impact sent vibrations through his body, but he didn't stop, couldn't stop. The Divine Sword moved faster than thought, redirecting, deflecting, destroying.
He descended through the heart of the vortex, his blade tracing a path of deflections that allowed his body to pass untouched. His feet hit the ground ten feet from Kokushibo, smoke rising from his clothing where near-misses had scorched fabric.
"Your techniques are impressive," Akira said, breathing harder now. "But they all have the same flaw."
"And that is?"
"They assume your opponent will retreat."
Before Kokushibo could process the words, Akira closed the distance with "Do-Ryūsen!"—a ground-level sweeping slash designed to destroy footing. Kokushibo leaped backward, and immediately the Sixteenth Form activated. Moon-Bow, Half Moon.
The demon's transformed blade swung upward, and six massive curved slashes materialized, crashing down several meters ahead of him like falling guillotines. Each one carved a crater three feet deep, the shockwaves kicking up clouds of dust and debris. The technique was designed to catch fleeing opponents, to punish anyone who tried to maintain distance.
But Akira wasn't fleeing.
He ran forward, directly into the falling slashes. His blade rose, intercepting the first crescent with a parry that sent him skidding sideways. He rolled, came up under the second, deflected the third with a rising slash that sent sparks showering. The fourth grazed his back, drawing blood. The fifth he avoided by dropping flat and sliding beneath its arc. The sixth—
He caught it on his blade with both hands, the impact driving him to one knee. The crater formed around him, the ground cracking and crumbling. But he was still moving, still advancing through the destruction.
Kokushibo's six eyes registered something that might have been respect. "You do not know... when to retreat."
"Retreat is death," Akira said, rising from the crater. "Against you, hesitation is death. The only way forward is through."
They clashed again, a rapid exchange where techniques blurred together. Moon Breathing and Hiten Mitsurugi-ryū, demon and Viltrumite, flesh-blade and Divine Sword. Each strike carried enough force to shatter stone. Each parry sent shockwaves rippling outward.
But Akira was beginning to understand. Four hundred years of perfection had made Kokushibo's movements refined to the point of predictability. Each form had optimal ranges, specific rhythms, telltale shifts in breathing that preceded their activation. The Moon Breathing was devastatingly powerful, but it was also...
Memorized.
Perfected to the point where innovation had ceased.
Living technique versus fossilized mastery.
"You're holding back," Kokushibo said suddenly, all six eyes narrowing. "Your speed, your strength—you haven't shown everything."
Akira's smile was sharp. "Neither have you."
"Then let us both..." Kokushibo's killing intent crystallized the air itself, "show our true forms."
The demon's aura erupted like a physical force, dark and suffocating. His six eyes blazed with golden light. His transformed blade pulsed, growing additional crescent edges that seemed to multiply even as they were watched.
Akira's response was simpler. His stance deepened. His breathing steadied to a rhythm older than this world. The Divine Sword hummed, recognizing the approach of its true purpose.
The Hiten Mitsurugi-ryū was created to protect. But at its heart lay a single technique designed to kill—an attack so fast, so overwhelming, that even seeing it coming changed nothing.
The ultimate technique.
Amakakeru Ryū no Hirameki.
The Dragon Flight of Heaven.
Akira's left foot slid back, his weight distributing with precise calculation. His sword rose to shoulder height, angled slightly downward. Every muscle in his body coiled like a compressed spring. His breathing slowed to a single, deep inhalation.
Kokushibo's eyes widened. "That stance... it's different. What—"
Akira moved.
The world couldn't contain his speed. The Viltrumite physiology combined with Hiten Mitsurugi-ryū's ultimate technique created motion that transcended human possibility. He crossed the distance in less than a heartbeat, his blade already in motion, the draw and strike executed as a single action.
Kokushibo's six eyes saw it coming. They processed the trajectory, calculated the counter, prepared the parry. His transformed blade rose to intercept, the perfect defense against a perfect attack.
But the Amakakeru Ryū no Hirameki had a second strike.
The instant Kokushibo committed to his defense, Akira's back foot kicked off the ground, generating a secondary burst of acceleration that should have torn human muscles apart. His blade withdrew a fraction of an inch from Kokushibo's parry and then thrust forward again on a new trajectory, this time aimed at the neck from an angle that bypassed the demon's defense entirely.
The technique existed in two moments—the feint and the true strike—but executed so quickly they appeared simultaneous.
Kokushibo's eyes registered the change too late.
The Divine Sword passed through his neck like light through water.
Time seemed to suspend. Kokushibo's body stood motionless, his transformed blade still raised in defense. Then his head separated, tumbling backward in a lazy arc before hitting the ground and rolling to a stop.
Akira landed behind the demon's body, his sword held low in the follow-through position. He didn't turn around. Didn't need to.
"It's over."
Kokushibo's body remained standing for three heartbeats. Then it collapsed, folding at the knees and crashing face-first into the torn earth.
The head lay six feet away, all six eyes wide with shock. The mouth moved, sounds emerging without breath to carry them properly. "How... that speed... that second strike..."
Then the regeneration began.
Flesh sprouted from the severed neck, tendrils of organic matter reaching upward like grasping fingers. More tissue emerged from the head, crawling across the ground toward the body. The regeneration of an Upper Moon was legendary—even decapitation couldn't guarantee death.
Kokushibo's head pulled itself across the ground using the tendrils, slowly but steadily returning to reunite with its body.
"You... have not won..." The voice was distorted, wrong, but carried the same calm certainty. "I will regenerate... and then..."
Akira turned, crouched down next to the crawling head, and met those six frantic eyes with a flat expression.
"You won't."
"What?"
"This sword." Akira held up the Divine Sword, its crimson blade still humming with power. "It's not like a red nichirin blade. It's something far more lethal."
Kokushibo's tendrils slowed, his regeneration faltering. All six eyes fixed on the blade with sudden understanding and mounting horror. "No... that's impossible... there's nothing like that in existence..."
"You're right. There isn't. Not in your world, anyway." Akira's smile was cold, devoid of warmth. "You know what's funny? This entire fight, I was holding back."
"Lies..." The word came out as a hiss.
"The truth is simpler and crueler." Akira stood, looking down at the dying demon with something resembling pity. "You were too weak. Even as a demon who's trained for four hundred years, who reached Upper Moon One through skill and dedication... you died by someone stronger than you."
"No..." The regeneration was failing now, the tendrils disintegrating into ash. "No, I am... Can't be weak..."
"You were" Akira sheathed his sword with a quiet click. "And so am I"
Kokushibo's body began to crumble, the disintegration spreading from the severed neck downward. His head experienced the same fate, flesh flaking away like burned paper caught in wind. But his eyes—all six of them—remained fixed on Akira until the very end, burning with questions that would never be answered.
The Upper Moon One, the demon who had terrorized the world for four centuries, the swordsman who had perfected Moon Breathing to impossible heights... reduced to nothing but scattered ash drifting on the wind.
Akira stood alone in the ruined clearing, surrounded by shattered trees and carved earth. The moonlight painted everything in shades of silver and shadow.
Behind him, he heard footsteps approaching—hesitant at first, then more confident.
"Akira-san..." Tanjiro's voice trembled with awe and disbelief. "You... you actually..."
"Told you I'd win."
Tamayo stopped beside the pile of ash, her eyes studying it with the careful attention of someone who'd spent centuries understanding demons. "Upper Moon One," she whispered. "Defeated so... easily."
Yushiro stared at Akira like he was seeing him for the first time. "What are you?"
"Don't make me state the obvious, Yushiro" Akira sighed.
Nezuko approached the ash pile cautiously, her eyes wide. She reached out slowly, her fingers passing through the remains. They disintegrated at her touch, scattering completely.
"It's really over," Tanjiro said, the words hollow with shock. "Upper Moon One is... gone."
"One down," Akira said, starting to walk past them. "How many more until we reach Demon Slayer Corps?"
Tamayo watched him go, her expression complex. She'd lived for over four hundred years. She'd seen Yoriichi Tsugikuni, the man who nearly killed Muzan and who remained the measuring stick by which all demon slayers were judged.
Akira had just that level of commitment and skills in front of them.
And somehow, looking at his retreating back, she suspected he hadn't been lying about holding back.
The thought was both terrifying and oddly comforting.
If anyone could kill Muzan Kibutsuji, it was the man walking ahead of them, his red sword catching the moonlight like a promise of death yet to come.
. . .
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