"Thunder Breathing, First Form: Thunderclap and Flash!"
Zenitsu Agatsuma poured every ounce of his strength into one leg and released it in a single explosive surge. His body tore through the air like a bolt of lightning, closing the distance to the demon in a blur too fast for the eye to follow. His Nichirin Sword flashed free in that same heartbeat, slicing clean through the demon's neck and sending its head tumbling to the ground.
He stared at the severed head, at the grotesque, snarling face frozen in its final moment of rage. Terror flooded him—raw, choking fear that made him want to bolt, to curl up and sob until it all went away.
But he didn't run. Every scrap of dread, every dark impulse screaming at him to flee, he crushed it down right there and then.
The old Zenitsu had always turned away from his own cowardice and helplessness. He had run, hidden, avoided everything that frightened him. He could no longer stand the sight of that version of himself.
"I… I admit it. I'm terrified of dying. I'm so scared I can barely breathe. But… but even so…"
Zenitsu lifted his head, eyes burning a fierce crimson as he fixed the beheaded demon with an icy stare.
His teacher—the man he had always looked up to with such pride—had been slaughtered by a powerful demon. His senior, the one who had scorned and belittled him at every turn, had died the same way. The strict yet gentle grandfather who had raised him was gone. The entire mountain was empty now; only he remained.
"From this day forward, I refuse to be that sniveling coward anymore."
He sheathed his blade with a quiet click and watched in silence as the demon's body crumbled into ash and scattered on the wind. Hand resting on the hilt of his sword, Zenitsu turned and walked deeper into the night. He was going to hunt the very creatures he had once feared more than anything—the demons he had desperately wanted to escape.
...
"Boar Rush! Boar Rush!"
The boy wearing the wild boar's-head mask charged through the forest at breakneck speed, twin serrated blades gleaming in each hand, sending the underbrush crashing in his wake.
Ahead of him, a demon scrambled and fled in a blind panic, its crimson eyes wide with pure, animal terror.
"Stop running and fight me like a real opponent!"
Inosuke Hashibira roared with excitement as he closed the gap.
A brilliant flash of steel cut through the air behind the demon. It collapsed mid-stride, head already severed.
"Pathetic. Barely worth the swing," Inosuke muttered, sliding his blades back into their sheaths on his back and tugging his boar mask into place.
Moonlight slipped between the leaves, painting shifting patterns across his bare shoulders and back.
The demon's corpse began to break apart, dissolving into ash that the breeze carried away.
After the kill and the frenzied chase, exhaustion finally caught up. Inosuke dropped right where the demon had fallen, crossed his arms, and settled in for a rest.
A familiar dream drifted over him.
He was tiny, cradled in warm arms. Something soft brushed his cheek—tears or a smile, he could never quite tell. A voice, faint and blurred, urged him to live, to keep living no matter what. Someone important. Someone he could never forget.
"Why do I keep dreaming about this?" Inosuke Hashibira stood up and irritably scratched at his head.
Then, in the very next instant, the instincts he had honed like a wild beast suddenly screamed through his body. Every muscle tightened violently as he bent low on reflex, his posture dropping like a predator preparing to pounce. His hands snatched the twin Nichirin Swpord from his back and slashed out in one fluid motion.
Clang!
A metallic collision rang sharply through the forest as sparks burst into the air.
Almost simultaneously, Inosuke twisted around and launched a fierce counterattack toward the person who had approached him.
Having spent years surviving in the mountains and wilderness while mimicking the habits of beasts, he had developed his own unique Breathing Style—Beast Breathing. Combined with his monstrous physical abilities, his dual blades struck with terrifying speed.
And yet—
no matter how fast his swords were, they could not so much as graze the newcomer's clothing.
A young girl wearing a fox mask with closed smiling eyes gracefully evaded his attacks while quietly observing the boy before her. As she measured his strength, she gradually became certain that this was likely the Inosuke Hashibira that Soma had instructed her to find.
Boom!
Another slash crashed into empty space before cleaving into the ground, kicking up dirt and dust in all directions.
Panting heavily, Inosuke finally stopped and lifted his head, glaring at the girl who had already leapt onto the treetop above him, lightly standing upon the swaying branch.
"Hello…" Makomo spoke softly as she looked down at him. Her voice was gentle and strangely ethereal.
But Inosuke had no interest in listening. All he wanted was a proper fight against this person, yet her speed was so absurdly fast that he could not land a single hit on her, and that frustrated him to no end.
"Get down here and fight me already!" Inosuke roared angrily.
"I came to invite you to join the Demon Slayer Corps and hunt demons with us." Makomo spoke calmly, as though she hadn't heard his challenge at all.
Inosuke scratched his head again and tightened his grip around his swords. "Fight me first!"
"Boar Rush!"
Without hesitation, he rammed directly toward the massive tree Makomo was standing on.
"Bang—!"
His head slammed into the trunk with a heavy, muffled impact, causing the entire tree beneath her feet to shake violently.
Seeing this, Makomo's mouth slowly parted in stunned disbelief.
Just as Soma had said…
this person really wasn't very bright.
...
The underground laboratory was thick with the sharp scent of disinfectant.
Rows of shelves lined the room, filled with countless reagents and glass containers, while nearby cabinets held all kinds of petri dishes and experimental samples.
Inside this dim underground chamber, a gentle-looking woman and a petite young girl were carefully conducting research on a newly developed medicine.
"Only the final step remains now… we just need to wait for the cells to fully fuse together," Shinobu Kocho murmured, her striking purple eyes locked on the liquid slowly merging inside the petri dish.
"The fusion rate is slower than we expected," Tamayo observed quietly, though her gaze sparkled with excitement. Having Shinobu's help had accelerated their research beyond anything she had imagined possible.
As she spoke, Tamayo carefully added a single drop from a test tube. The liquid inside the dish shifted dramatically—from deep violet to a translucent amber almost instantly.
"Cellular activity is decreasing... regenerative capacity is declining as well..."
Both women held their breath as the readings came in.
After a long, tense wait, the serum finally stabilized.
"Did it succeed?" Shinobu asked, looking up at the vial in Tamayo's hand.
"I'm not certain, but we can test it now."
Tamayo pressed her lips together, excitement flickering in her eyes. Barely able to contain herself, she immediately carried the medicine deeper underground toward another chamber.
Inside the room, a demon was imprisoned beneath heavy chains.
The moment it heard footsteps approaching, its eyes snapped open.
"Graaah...!"
The demon let out a savage roar almost immediately.
Yet beneath those crimson eyes flashed unmistakable fear.
After being used as an experimental subject time and time again, the captured demon had long since become terrified of Tamayo and Shinobu to the very core.
Shinobu paid no attention to any of that and immediately injected the medicine into the demon's body.
The instant the solution entered its bloodstream, the demon's body arched violently.
"ROAAAR—!"
Its limbs convulsed uncontrollably as the chains binding it rattled and clanged. Iron shackles scraped harshly against the concrete pillars, producing a shrill, grating sound.
Changes began to spread across the demon's skin at a rate visible to the naked eye.
Unlike the healthy coloration produced during previous experiments, what emerged this time was a withered, decaying gray. Deep cracks spread across its flesh like parched earth scorched beneath a relentless sun.
Shinobu instinctively stepped back, her eyes never leaving the test subject.
The demon's hair was falling out.
Strand after strand drifted downward, streaked with gray and white, landing upon the dusty floor below.
Its back gradually hunched over as its joints emitted sharp cracking noises, resembling a rusted machine being forced to operate beyond its limits.
The face that had still retained traces of youthful features began collapsing inward at an alarming pace. Its cheekbones protruded sharply, its eye sockets sank deep into its skull, and loose skin sagged downward, forming layer upon layer of deep wrinkles.
Aging?
"Tamayo!" Shinobu's voice sharpened.
Tamayo's eyes stayed fixed on the demon." Aging symptoms... the cellular telomeres are shortening at an extreme rate. The number of cellular divisions is reaching the lifetime limit of an ordinary human within mere seconds..."
Her voice trembled with barely contained excitement.
The demon's struggles grew weaker.
It wasn't sedation. Its body was simply failing.
Muscles withered, bones turned brittle. Even the rattle of the chains sounded dull and powerless. Every breath came in a hoarse, wheezing rattle like a broken bellows.
"It's still aging," Shinobu murmured.
As she spoke, she drew her Nichirin Sword.
A flash of steel streaked through the air.
The blade cleanly severed the demon's left arm.
The cut was flawless. Dark-red, viscous fluid slowly seeped from the wound, resembling stagnant blood left untouched for years.
The severed arm hit the ground. Its fingers twitched a few times before becoming completely still.
Then both women held their breath.
No regeneration.
At the cross-section of the severed limb, where flesh should have been frantically growing and writhing back together, only a small amount of tissue fluid slowly seeped outward.
The skin surrounding the wound had turned a lifeless gray.
There were no signs of healing.
Even the most basic clotting response appeared sluggish and weak.
A faint groan escaped the demon's mouth.
It no longer sounded like a demon.
Instead, it resembled the exhausted sigh of an elderly man lying on his deathbed.
"Regenerative ability… completely gone," Tamayo breathed.
Shinobu slowly sheathed her blade, her gaze resting on the demon's face, now so aged that it was nearly impossible to recognize its original appearance.
Its eyes remained open.
Yet the crimson color had largely faded, replaced by a murky yellow-gray clouded with blood vessels.
The eyes of an elderly human.
"The effect is still present, but it's weakening. Regeneration is beginning to return… vitality is recovering," Shinobu said, frustration edging her tone.
"It seems to have a limited duration," Tamayo noted.
"It will need further refinement."
Shinobu clenched her fist, eyes alight. "Even so, if we managed to inject something like this into that demon, it would leave him far more vulnerable."
Without another word she swung her blade again, decapitating the creature and ending the experiment.
Tamayo glanced at her. Shinobu's hatred for demons ran so deep that the moment a subject lost its research value, she ended its existence without hesitation.
...
Giyu Tomioka had spent days standing at the water's edge, quietly contemplating the ultimate secret of Water Breathing that Soma had described to him.
He closed his eyes and let the world fill his senses.
A gentle breeze stirred through the grass and trees, and the surface of the water rose with the wind, spreading out in ripples one after another.
The world seemed to fall into stillness at that very moment.
For an instant, Giyu Tomioka felt as though he were standing upon a calm stretch of water. Everything around him was motionless, as if even time itself had stopped.
"Drip…"
At some unknown moment, a single drop of water fell into the surface, sending ripples across the once-peaceful water.
And in that same instant, Giyu Tomioka's blade left its sheath.
"Water Breathing, Ultimate Technique: Eleventh Form—Dead Calm!"
The blade was drawn in a single instant, and even the howling wind that swept before him seemed to come to a standstill beneath this technique.
"So this is the ultimate secret technique of Water Breathing?"
Feeling the utmost calm within his own heart, and sensing that everything entering his range would be transformed into silent water, he finally experienced the state of absolute tranquility that Soma-san had spoken of.
He had finally comprehended it.
Even Giyu Tomioka, who had always been a man of few words, clenched his fist at this moment and could not help speaking aloud in excitement.
With that excitement held deep in his heart, Giyu Tomioka returned.
Along the way, quite a few people greeted him. Giyu only nodded in response and spoke very little.
On the road, Giyu Tomioka saw many swordsmen learning swordsmanship from a man named Himura Kenshin. He vaguely heard them mention something called Hiten Mitsurugi-ryu, Battojutsu, and the like.
He faintly felt that the other party was an extremely formidable master of the sword.
Perhaps sensing something as well, Himura Kenshin raised his head at that moment, gave a slight nod, and revealed a faint smile.
Giyu Tomioka also inclined his head slightly. From the man's body, he could vaguely sense an extreme sharpness, though he did not know whether that razor-edged offense could break through the ultimate technique of his own Water Breathing.
…
Soon Giyu reached the courtyard and stepped inside.
The moment he entered he saw Kanao Tsuyuri—black hair with purple eyes and pink-tipped ends tied in a single side ponytail—sparring with Nezuko.
The speed of the two was extremely fast, so fast that afterimages were left behind in the air. Ordinary people would likely be unable to see their movements clearly at all.
"They're getting stronger and stronger."
Giyu Tomioka sighed inwardly. These two girls who followed beside Soma-san seemed to have their strength increasing almost every single day.
Seeing Giyu Tomioka arrive, Soma was also slightly surprised. During these days, Giyu Tomioka had been staying by the waterside almost all the time and rarely came out.
"Judging by the look of you, you should have gained some insight?" Soma asked with a smile.
"Mm." Giyu Tomioka nodded. As someone who spoke very little, he did not even say that he had comprehended "Dead Calm."
"Congratulations." Soma smiled, then said, "Perfect timing. In a few days, there will be a mission to carry out, and I will be leading it. When the time comes…"
Giyu Tomioka was slightly surprised, as it was rare to see Soma take action personally.
Soma had just been about to explain that the mission to hunt down Upper Rank Two, the Ice Demon Doma, had been assigned to him—and that he was planning to invite Giyu Tomioka to join them—
when a voice suddenly came from outside the door.
"Ah… I finally made it."
Soma turned his gaze toward the entrance.
A tall and slender young girl stood beneath the sunlight. Her delicate features seemed especially bright and radiant, while her pink hair, fading into green at the tips, swayed gently in the breeze.
Mitsuri Kanroji.
She had come at Soma's invitation to participate in the encirclement and hunt for Upper Rank Two, the Ice Demon, Doma.
"Hello! Um… is this Soma-san's residence?" Mitsuri Kanroji asked curiously.
...
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