The black stone of the arena quaked violently as Iguro Obanai's demonic aura surged to its peak. His twin curved blades crossed before his chest, serpent markings spreading madly along his arms as pale violet venom mist intertwined with shadowy black serpents, forming the image of a monstrous phantom snake.
It was the ultimate fusion of Serpent Breathing and his Blood Demon Art—his killing move.
"Serpent Breathing: Secret Technique—Infernal Serpent Devours Heaven! Blood Demon Art—Ten Thousand Serpents!"
The giant serpent phantom opened its massive jaws, venom dripping from its fangs with a hiss. The sheer pressure of its killing intent seemed enough to swallow everything in its path.
Where the serpent passed, even the air screamed under the crushing force. The black stone floor split into deep gouges from its scales, and the surrounding light seemed devoured by the malice that radiated from its form.
Giyu's eyes sharpened, his grip steady as the Nichirin Sword in his hand flared with three colors—rippling blue water patterns coiled around the blade, orange-red flames danced along its edge, and faint silver moonlight traced the spine of the sword. The three Breathing styles merged in perfect harmony, their energies intertwining without a single clash.
"Tri-Element Slash—Water, Moon, and Flame: Shatter Illusion!"
His blade arced upward in a perfect crescent. The flowing grace of Water Breathing deflected the serpent's charge, the searing heat of Flame Breathing scorched its body, and the cutting precision of Moon Breathing pierced straight through its eyes.
A sharp tearing sound split the air as the blade struck true. Venom sprayed outward, and the serpent's roar filled the arena before its body shattered into fragments of black mist that scattered and vanished.
Obanai was thrown back five steps by the blast, his twin blades trembling in his hands. The wounds on his arms split open again—his regeneration had always been slower than other Upper Moons since he had never consumed human flesh. The immense energy drained by his ultimate technique left him weakened, his black blood seeping sluggishly from the gashes, unable to clot. Every swing of his blade sent jolts of pain through his body.
"Dammit…"
He clenched his teeth, his scarlet serpent-like pupils burning with frustration. Ignoring the pain, he kicked off the ground again, launching himself at Giyu. His blades swept in a twisting, unpredictable rhythm. "Serpent Breathing, Fifth Form—Slithering Serpent!"
His twin swords weaved left and right, thrusting and slashing in chaotic succession, their erratic motion meant to disrupt Giyu's flow and break his defense.
But Giyu had already read his movements. Blue ripples burst along his blade. "Water Breathing, Fourth Form—Striking Tide!"
Each stroke flowed like an advancing tide, layer upon layer of waves crashing against Obanai's attacks. Every strike was precisely placed, intercepting the serpent-like blades head-on.
At the same time, Giyu shifted his footing, his movement smooth and fluid like flowing water, circling to Obanai's flank. Silver light gleamed across his sword. "Moon Breathing, Second Form—Pearl Flower Moongazing!"
Three arcs of slashing light crossed through the air, cutting toward Obanai's waist.
His eyes widened. He twisted away, but not fast enough—the edge of one crescent grazed his side, tearing open his ribs as black blood spattered across his clothes.
He staggered backward, the searing pain in his ribs making each breath labored. His once-graceful movements began to falter.
"Your regeneration is too slow," Giyu said calmly, his tone more observation than mockery. "You haven't eaten humans, have you?"
Obanai's entire body went rigid, then he gave a short, bitter laugh. "So what? Even without eating humans… I can still kill you!"
He was telling the truth. Even as a human, he had hated eating. After becoming a demon, despite his hunger and agony, his human restraint remained—he refused to consume human flesh. Instead, he hunted beasts in the mountains, feeding on animal blood and meat just enough to sustain his demonic energy.
But animal flesh was far inferior to human flesh. His regeneration lagged far behind that of other Upper Moons, and even his upper limit of demonic power had been restricted.
Taking another sharp breath, Obanai unleashed his Blood Demon Art once more. "Blood Demon Art—Serpent Shadow Step!"
His form dissolved into overlapping serpent shadows, darting toward Giyu's back for a surprise strike.
But this time, his movement faltered—his wounded ribs tugged against the muscles, causing a minute delay in his speed.
Giyu, drawing on his inherited future memories, had already foreseen his trajectory. Without even turning, he flicked his sword backward, his blade igniting in orange flame. "Flame Breathing, First Form—Unknowing Fire!"
The arc of flame sliced through the air like a meteor, striking directly into the serpent shadow.
With a loud crack, Obanai was forced out of stealth. His shoulder erupted in flame, the black fabric of his haori smoking as the fire bit deep into his flesh.
He stared at Giyu, and for the first time, fear flickered in his serpent-like eyes.
The man before him wasn't just fast or strong—he predicted every move, countered every strike, as if he could see through his very mind.
Obanai's breath came ragged. His twin blades hung limply at his sides, his demonic energy flickering weakly around him.
Giyu said nothing. He simply raised his sword once more. The tri-colored light along the blade burned brighter than ever, its brilliance filling the arena.
He could sense it—Obanai's presence was fading. His energy nearly gone. One final strike would end it.
But then—his mind trembled.
A fragment of memory flashed through the haze.
Tō, drenched in blood, shouting at him—"Giyu-sensei, stop going down the wrong path!"
Kamado Tanjiro gripped his Nichirin Sword tightly, his eyes full of anticipation.
At the same time, a voice inside his mind whispered wildly: 'Don't kill him. Don't eat him. He isn't the enemy…'
Iguro Obanai stared at Giyu, who had raised his blade. He closed his eyes and spoke in a calm tone.
"If you're going to kill me, do it. I won't beg. It's just a pity… I couldn't avenge Kyojuro, and I couldn't rid the world of a monster like you."
"Monster?"
Giyu's movement froze. The images in his head grew clearer, flashing faster and faster—fragmented memories flooding back, making his grip on the sword tremble.
He took a deep breath, suppressing the chaos in his thoughts, and swung his Nichirin Sword downward—
—but instead of Obanai's neck, the blade struck his twin swords.
A sharp metallic clang echoed through the arena as Obanai's twin blades were flung across the floor, embedding themselves into the black rock wall, the steel still vibrating faintly.
Obanai's eyes snapped open in shock. "You… why didn't you kill me?"
According to the rules of the Upper Moon replacement duel, the victor had every right to kill the loser—
to devour the defeated's demonic power and secure his rank.
Giyu didn't answer. He simply turned his back to Obanai, his voice hoarse—rougher than he realized.
"Leave. Don't appear before me again."
"What do you mean?"
Obanai forced himself upright, black blood seeping from his side.
Giyu's steps halted. That same voice echoed stronger in his mind now—'Don't eat. Don't eat. Don't kill.'
The sealed fragments of his memory surged like a tide, hammering against his consciousness—
Shinobu handing him the vial of medicine, Oyakata-sama's gentle smile, Tanjiro's bright, trusting grin…
His chest tightened painfully; even breathing became difficult.
"I'll say it again—leave."
Giyu's voice rose slightly. His grip on the sword was so tight that his nails dug into his palm.
He feared that if he stayed even one second longer, Kibutsuji Muzan's consciousness would sense something wrong.
Worse, he feared his own restraint would break, that the memories clawing at his mind would drag him into chaos.
Obanai stared at Giyu's back, his expression conflicted.
He didn't understand why Giyu had spared him—or that brief flicker of hesitation he saw in his eyes.
But he knew this was his only chance.
He picked up his twin blades and staggered toward the exit.
His figure faded into the darkness, swallowed by the shadows of the Infinity Castle.
Giyu remained motionless until Obanai's presence completely vanished. Then, slowly, he lowered his sword.
He pressed a hand against his temple. The storm in his head finally calmed, but a single thought rooted deeper in his heart:
'Don't eat. Don't kill. Protect them…'
That thought was like a seed planted deep in his soul.
Even buried under Muzan's seal, it refused to die.
He looked down at his hands—Obanai's black blood still smeared across his skin.
Disgust flickered in his eyes. He wiped it away roughly and turned toward his room.
Only the scattered stones and black stains on the floor remained, silent witnesses to the fierce battle that had just taken place.
…
Inside his room, Giyu sat by the window, staring into the endless darkness beyond.
He didn't know why he had let Obanai go.
He didn't know why those fragments of memory had surfaced.
But he knew one thing—he was drifting away from the path Muzan had carved for him,
moving toward something unknown.
"…Tomioka Giyu."
He whispered the name softly again. A faint ache pulsed in his chest.
He tightened his grip on his Nichirin Sword. Faint blue ripples of water shimmered across the blade.
Perhaps what the future Giyu had said was true. His memories—his emotions—had not been completely erased.
They were merely waiting for the right moment to awaken.
And that moment might come soon—when he crossed paths again with Tanjiro and the Demon Slayer Corps.
…
In another chamber of the Infinity Castle, Kibutsuji Muzan closed the report sent by one of the lower demons.
Disappointment flickered in his crimson eyes. He had expected Mushiki to devour Yatsuki after winning the replacement duel.
This was the second time. The second time Mushiki had refused to consume another demon.
Those memories were sealed by Muzan himself, bound so tightly that no one—least of all Mushiki—could break them.
With a faint sigh, Muzan murmured,
"Mushiki… I thought you would become my sharpest blade. I didn't expect you to still cling to that worthless human instinct."