Chapter 194: Breath of the Demon
Half a day later, Kyojuro squatted on the ground, his rough hands braced heavily against his knees. His chest heaved like a broken bellows.
His face burned a deep, flushed red. Heavy drops of sweat rolled down his forehead, striking the stone slab below with rhythmic, wet slaps. Inside his chest, his lungs felt as though someone had shoved a live coal down his throat. The heat was suffocating, expanding against his ribs until he thought they might crack.
He had failed again.
He could barely manage the absolute basics of the Sun Breathing techniques that Yoriichi had demonstrated for him. Even pushing his physical limits to the absolute brink, he could only maintain the proper circulation for about twenty breaths.
Once he crossed that threshold, his lungs screamed in agony, threatening to burst outright. He had no choice but to break the form and gasp for normal air.
"Not right... still not right..."
Kyojuro panted, his thick brows knitting together in deep frustration. He raised a calloused hand and thumped it hard against his own chest, trying to dislodge the lingering, suffocating heat trapped inside.
The fundamental core of Sun Breathing required the user to integrate the sheer, unyielding heat of the sun into their internal breathing cycle. However, forcing that kind of solar energy into the bloodstream demanded a body with an impossibly high tolerance.
Body temperature skyrocketed. Blood flow accelerated to a terrifying degree. The load on the heart increased sharply. The fragile bodies of ordinary humans simply could not withstand the sheer violent pressure of it all.
Yoriichi could do it flawlessly because he had been born for it.
The Transparent World granted the legendary swordsman absolute, microscopic control over his own internal state. He could perfectly regulate the thickness of every single blood vessel and the exact tension of every muscle fiber, mitigating the destructive heat before it could cause harm.
Kyojuro did not possess that divine talent.
He could only rely on the mortal body he had rigorously trained every single day of his life. Among ordinary people, his physique was considered monstrously strong, but throwing himself recklessly at a technique meant for a god was clearly not enough.
"Kyojuro."
Yoriichi crouched down beside the gasping young man. Those deep, serene red eyes looked at him with absolute calm. "Sun Breathing... perhaps it does not suit you."
The words were delivered with blunt directness.
But Yoriichi was always like this. He did not know how to sugarcoat the truth, nor would he ever tell a lie just to spare someone's feelings.
Kyojuro froze, his heavy panting hitching in his throat.
"Not suitable?"
"Everyone's body is fundamentally different."
Yoriichi stood up smoothly, his own Nichirin Blade resting casually against his shoulder. "I think of Sun Breathing as the sun itself. There is only one sun in the sky, but when its light shines down upon different places, it reflects entirely different colors."
He looked down at the exhausted swordsman.
"You do not need to learn how to become the sun."
"You need to find the light that belongs uniquely to you."
Kyojuro fell completely silent.
The light that belonged to him.
He slowly lowered his head, staring at his upturned palms. They were rough, covered in thick calluses and layered with old, faded scars from years of relentless swinging.
An image suddenly flashed through his mind.
Those same hands had held torches countless times. When tracking flesh-eating demons through the pitch-black, freezing depths of the mountain forests at night, the roaring torch had always been his only source of light.
Flames, burning fiercely against the dark.
"Flame..."
He whispered the word out loud, tasting the ash and heat of it on his tongue.
His family surname, Rengoku. Did it not literally mean purgatory? Was that not just another, more intense manifestation of flame? It was the very blood and heritage flowing through his family's veins.
Yoriichi glanced at the spark returning to the young man's eyes and offered a faint, encouraging smile.
He nodded once. "Try it."
Across the sunlit courtyard, Hikaru no longer paid any attention to their training session. The undead Oni Samurai simply closed his eyes and sat cross-legged on the smooth stone platform, his posture rigid and perfectly still.
The newly forged Nichirin Blade lay quietly across his knees.
In just a short span of time, the system favorability had ticked up from sixteen to eighteen.
It was not incredibly fast, but it was not agonizingly slow either.
The inherent power of sunlight trapped within the Nichirin Blade absolutely refused to accept his Yao Qi. They reacted like two magnets of the exact same pole. The closer Hikaru tried to force them together, the more violent the repulsive force became, threatening to violently reject his demonic energy.
However, the dark, demonic fire burning within his core would occasionally brush against the Nichirin Blade and produce a momentary, microscopic resonance. It was an extremely brief, fleeting connection.
In that fraction of a second of resonance, the dormant power of sunlight inside the steel began to accept him, briefly treating his monstrous energy as one of its own.
Hikaru was a pragmatic creature. He was ruthlessly using these sporadic, tiny windows of resonance to infiltrate the blade's core little by little.
It was exactly like water slowly dripping through solid stone. Patience and relentless grinding.
But at this exact moment, his cold, calculating attention was not entirely focused on wooing the Nichirin Blade.
His mind was simultaneously dissecting another matter entirely. He was mentally breaking down the entire complex structure of Yoriichi's Sun Breathing, which he had perfectly memorized with a single glance of his Crimson Demon Eyes.
Remembering the forms and actually being able to use them were two entirely different concepts.
Because his lungs were dead.
As an Oni Samurai, his original human body had completely died the moment he transmigrated into this world.
Later, he had relied entirely on the system to resurrect him, relying on the dark Yao Qi to drive his stiff limbs, and relying on gruesome mutation after mutation to gradually claw his way back to life. But that 'life' was strictly an outside-in process.
At least for now, the vast majority of his internal organs were still rotting and dead.
Only his demonic blood was actively changing, and his reinforced bones were growing denser.
Apart from that, the beating heart and functioning kidneys inside him were merely temporary, magical projections generated by the Asura Transformation.
And his lungs, the vital organs entirely responsible for the act of breathing, were completely withered and dead.
He did not actually need to breathe to survive. Every single rise and fall of his chest was just a hollow illusion simulated by his Yao Qi to mimic human behavior. Air entered his dead lungs and was pushed back out, but the actual biological process of oxygen exchange did not exist at all.
Therefore, it was a biological impossibility for him to learn Sun Breathing.
That supreme technique was entirely established on the biological function of a living, breathing human's lungs. It required real gas exchange. It required drastic changes in blood oxygen concentration to forcibly drive the explosive improvement of bodily functions.
But what if he simply ignored the path of Sun Breathing altogether?
The core concept of Sun Breathing was the sun itself. The sun belonged to the concept of Yang, to roaring fire, to vibrant life.
That was Yoriichi's path. It was the path of the living.
Hikaru was a monster. He was an Oni. He had not yet officially crossed the boundary back into the world of the living.
Sun Breathing shone down upon all living things, bestowing immense power upon those who walked under the sky. It was undoubtedly a breathing technique born of the heavens.
Hikaru did not belong to the heavens.
He belonged underground.
He existed in the dark, bloody crevice between the Underworld and the human world. He stood exactly at the boundary line separating death and life.
For an existence that had already died once to try and imitate the breathing of the blazing sun was inherently a foolish, futile effort.
However... what if, instead of trying to borrow light from the heavens above, he were to draw energy from the cold earth beneath his feet? What if he drew power directly from the imagined depths of the Underworld?
Substitute the blazing sun with the freezing Underworld. Substitute fresh air with thick Yao Qi. Substitute the racing pulse of the living with the stagnant, heavy pulse of the dead.
Sun Breathing was the living breathing the sun of the heavens.
Then he would simply breathe the Underworld beneath his feet.
The pragmatic idea rapidly took solid shape in his mind.
Hikaru opened his eyes. The complex purple patterns and glowing orange streams of light within his Crimson Demon Eyes flared to life simultaneously, casting a sinister glow over his pale face.
He slowly raised his hand, resting it on his knee with the palm facing upward.
Then, he took a breath.
It was not inhaled using his withered lungs, but forcibly dragged in by his Yao Qi. The dense demonic aura coating the surface of his skin contracted violently, acting like a massive vacuum. It forcefully sucked the heavy, scattered Turbid Qi lingering in the surrounding air directly into his body.
The freezing Turbid Qi rushed into his mouth and nose, flooding down into his dead lungs.
The lungs themselves did not expand or move, but the Yao Qi inside them certainly did.
The heavy Turbid Qi began to rapidly rotate and condense within the withered, remaining structures of his respiratory system. It coiled and swirled with violent force, forming an extremely small, highly concentrated vortex of dark energy.
That vortex spun relentlessly.
It was slow. It was incredibly heavy. It carried the absolute chill and crushing thickness of the Turbid Qi that existed between heaven and earth. Unlike the explosive, outward expansion of the sun's heat, this energy felt like it was constantly sinking downward. It mimicked the crushing gravitational pull of the legendary entrance to the Underworld, desperately trying to drag everything around it into a deeper, darker place.
There was no explosive expansion of scorching light like in Sun Breathing.
There was only an endless, suffocating sinking.
Sinking beneath the cold earth. Sinking deep into the silent kingdom of the dead. Sinking into that eternal, lightless darkness to which all living things would eventually return.
It felt exactly as if a heavy iron door to the Underworld had been cracked open inside his own chest.
After the inhaled Turbid Qi completed a full, agonizingly slow rotation within his dead lungs, it was forcefully pushed back out by the Yao Qi. But at the exact moment it was expelled, that Turbid Qi was no longer the same scattered energy it had been before.
It had been perfectly filtered.
Refined. Purified.
It had been forcibly compressed into a much denser, far purer form of Yao Qi. It was now a highly concentrated fuel, perfectly suited for a monster to absorb and use to drive a demonic body to its absolute limits.
If Sun Breathing was the warm grace bestowed by the sun upon the living, shining upon all things and making them grow strong.
Then Hikaru's new breathing was the freezing grace bestowed by the Underworld upon the dead. It settled all things, stripping away their warmth and causing them to return to their silent roots.
His lungs did not breathe oxygen, yet they could perfectly filter and purify the raw Turbid Qi of heaven and earth before outputting it as pure power. It mirrored how the dark road to the Underworld, despite being a path of absolute death, was also the necessary starting point for the reincarnation of all things.
One existed in the heavens, one existed deep in the earth.
One gave vibrant life, one governed absolute death.
The ultimate end of Sun Breathing was blinding light.
The ultimate end of Breath of the Demon was absolute silence.
The Transparent World that Yoriichi possessed from the moment he was born allowed him to perfectly master the breathing of the sun. He was a living person, the chosen child deeply favored by the sunlight itself.
But Hikaru had already died once. His lungs were dead. The vast majority of his body was dead. Therefore, the breathing of the Underworld was the only breathing technique that truly belonged to him.
The living breathe sunlight.
The dead breathe the Underworld.
Each walks their own distinct path. Each has their own ultimate peak to reach.
This was... Breath of the Demon.
Demon Breathing.
It was not the act of breathing air, but the act of breathing the Underworld itself.
Using dead, withered lungs as a blazing furnace. Using heavy Turbid Qi as the raw material. Using Yao Qi as the catalyst for conversion.
Inhaling, refining, circulating.
And at the exact moment this very first cycle of Breath of the Demon was successfully completed.
Deep within his chest cavity, those long-silent, dead lungs suddenly flashed.
It was extremely brief.
A dense mass of dim, eerie light, shifting between pitch black and sickly purple, suddenly took physical shape at the exact location of his lungs. It looked exactly as if a jagged entrance to the Underworld had cracked open a tiny seam right between the two withered organs.
And then.
It instantly went out again.
It flashed brightly and then died into nothingness.
Something was still missing.
Missing...
[Nichirin Blade (Favorability: 32. Unlocked first talent 'Oni Slayer'. Special attack against demons). Original wish for birth: 'Oni Slayer']
He was missing the full favorability talent.
Hikaru understood immediately. His pragmatic mind connected the dots without hesitation.
The Nichirin Blade resting on his knees was currently only a semi-Demonic Tool. It was not a fully formed, awakened Demonic Tool. If he relied solely on the talent ability brought by maxing out its favorability, it would be mathematically impossible for him to directly complete another full Asura Transformation projection.
But if he added the newly realized power of Breath of the Demon into the equation, it would be more than enough.
The Nichirin Blade and Breath of the Demon perfectly complemented each other's flaws.
The favorability had just jumped directly from eighteen to thirty-two in a single burst, and the resulting resonance between his body and the steel was incomparably intense.
But it was still not enough to push it over the edge.
Simple dialogue feeding and passive energy grinding also seemed entirely insufficient to make the stubborn blade reach 'full favorability' any faster.
It also required him to actually slay demons.
The fundamental reason for the Nichirin Blade's birth, the very core of its existence, was inherently to sever the twisted immortality of evil demons.
If he did not actively fulfill the bloody meaning of this sword's existence, the weapon would never truly accept him as its master.
That was not a problem that could be solved by simply pouring in more Yao Qi, nor could the blade's spirit be fooled by sweet talk and gentle handling. What the weapon desperately wanted was violent action.
The brief flash of Underworld light inside his chest just now undoubtedly indicated the correct direction.
The physical form of the Asura Lungs already existed within him. It just needed the right bloody conditions to fully awaken it.
And at the exact same time.
The extremely thin, chilling layer of dim mist that had overflowed from his body the moment Breath of the Demon took shape had caused a reaction. Although the mist was brief, it was already enough to bring about another drastic change.
He looked down at the Nichirin Blade resting in front of his knees.
The color of the steel blade had completely changed.
From its original, pale orange luster, the metal had rapidly darkened into an extremely deep, abyssal color that shifted constantly between pitch black and bruised purple.
It looked exactly like... the color of the Underworld itself.
This was the true origin of the name given to the color-changing blades.
Purple shining through deep black, black sinking endlessly into purple. That was a dark, heavy color that the warm sun could never possibly reach.
It was a color that only an existence that had already died once could ever be dyed with.
"From now on, I will call you Yomikiri."
Nichirin, Yomikiri. The Underworld Cutter.
Also known as... Immortal Severance.
It also happened to perfectly correspond with his other blades, Onikiri and Raikiri.
Over on the wooden corridor.
Kyojuro was still desperately trying to integrate the abstract concept of flame into his breathing cycle. Although he already had some vague ideas forming in his head, it was painfully clear that he had not yet found the correct physical pathway to execute it.
Thick veins bulged dangerously on the young man's forehead, and his face was still as violently red as a boiled shrimp.
Then, from the corner of his eye, he caught a sudden glimpse of the fleeting, dim-colored mist rolling off the stone platform across the courtyard. He also clearly saw the shocking scene of the Nichirin Blade's steel suddenly shifting into a dark, abyssal color.
And when he looked up, he saw the monster's eyes. In the glowing Crimson Demon Eyes that Hikaru had slightly opened, there was an added, deep brilliance. It looked exactly like staring down into the bottomless abyss of the Underworld.
Kyojuro's frantic movements instantly stopped.
He opened his mouth, completely stunned, then slowly closed it again. He turned his head mechanically to look up at Yoriichi.
Yoriichi was already looking over there.
For the very first time since Kyojuro had met him, a look of true, undisguised surprise appeared in those deep, serene red eyes.
Kyojuro's voice was slightly hoarse and deeply astonished. "Mr. Hikaru... have you already learned it?"
Yoriichi did not answer immediately.
But his eyes, currently seeing deep into the Transparent World, told him the absolute truth. A terrifying, fundamental change was indeed occurring within the core of that undead monster.
Although the physical change seemed currently incomplete, as if it had only just taken its first steps, the underlying structure was already almost deeper and vastly more complex than his own Sun Breathing.
That was not just a simple Breathing Style.
It was more of a complete biological metamorphosis that used the concept of breathing as a bridge to entirely reshape his internal energy circulation.
"Mr. Hikaru is a truly remarkable and extraordinary monster."
Yoriichi finally said in a low, quiet voice.
He offered no further comment on the matter.
In the corridor, Kyojuro remained squatting on the ground. He looked up at Yoriichi, then turned to look across the yard at Hikaru, and finally looked slowly down at his own calloused hands, which had yet to grasp even the basic method of his own style.
After a long, agonizingly silent while, he forced out a single, strained sentence.
"...What on earth am I even doing?"
That undead person had only seen a Breathing Style demonstrated half a day ago, and now he had already successfully created his own entirely unique, perfectly tailored version.
Yet here Kyojuro was, still coughing up his lungs like a sick child.
And that person was a literal monster, at that.
A monster... that was apparently vastly smarter than a human.
Kyojuro forcefully exhaled a heavy breath of Turbid Qi. His jaw locked tight. He clenched his fists until the knuckles popped, stood up straight again, and felt an overwhelming wave of stubbornness wash over him. He was completely unconvinced of his own failure.
After all, this burning feeling of being unconvinced, this refusal to yield, was precisely the raw fuel that the Rengoku family was best at using.
"Again!"
He shouted loudly at Yoriichi, his eyes burning with renewed fire. He took a massive, deep breath, forcing the heat back into his chest.
And immediately started coughing violently again.
Yoriichi watched him with a look of mild helplessness, while across the yard, Hikaru couldn't help but let out a low, dry chuckle at the display.
...
Meanwhile, in an entirely different part of the sprawling backyard of the Ubuyashiki Estate.
The Butterfly Kakushi sat quietly by the edge of the wooden veranda. A complete set of traditional tools for preparing medicinal herbs was laid out neatly in front of her. However, the heavy stone pestle in her hand had completely stopped moving. Her gaze was lifted, staring blankly across the dividing walls, as if she desperately wanted to see straight through the wood and into the neighboring courtyard.
She stayed frozen like that for a very long time.
Long enough that another figure, who had quietly walked up beside her, reached out and lightly flicked her on the forehead.
"What are you staring at so intently?"
The young woman with the thick, braided hair, one of the esteemed Hashira, stood by the veranda with a warm, teasing smile on her face.
"Sister, are you back already?"
The braided Hashira was undoubtedly the Butterfly Kakushi's older sister. They were biological sisters, yet their paths were vastly different. The older sister was exceptionally talented in combat and had already climbed the ranks to become a Pillar-level swordsman. Meanwhile, the younger sister was currently just a Kakushi member without any real talent for the blade. The gap in their status was massive, yet they clearly maintained a very close, loving relationship.
The braided Hashira smiled gently, her eyes crinkling. "I've been standing here watching you space out for a full quarter of an hour, you know?"
"I was just thinking about something."
"Thinking about what?"
"Thinking about..." The Butterfly Kakushi slowly turned the heavy pestle in her hands, her mind racing before she finally chose a more reasonable-sounding answer. "Thinking about what I saw earlier. The raw iron ore flowing down from the mountain all by itself."
The braided Hashira fell completely silent for a moment.
She had just returned from her perimeter patrol today and had already heard the frantic whispers about the incident from the other corps members. Seventy-two perfect Nichirin Blades completed in a single day. All the heavy ore marching into the blazing furnace entirely by itself, with the master Blacksmiths just standing around watching the show the whole time.
Her initial reaction at the time was naturally that it was completely impossible.
As a Pillar-level swordsman, she had personally visited the hidden Swordsmith Village many times to have her weapon maintained. She knew better than anyone exactly how incredibly difficult and time-consuming it was to forge even a single Nichirin Blade.
But after hearing the full, detailed story from the terrified witnesses, and personally seeing the seventy ownerless Nichirin Blades neatly filling the estate's warehouse, she could only remain silent in shock.
However.
"What's there to think so hard about?"
The braided Hashira reached out and affectionately tapped her younger sister's head again. "That person is a highly esteemed 'guest' whom even our great leader respects very much. It's not our place to question his methods."
She sounded completely indifferent to the matter.
But the Butterfly Kakushi knew her older sister well enough to know she was lying through her teeth. After all, for any dedicated swordsman of the Demon Slayer Corps, an extra, perfectly forged Nichirin Blade meant an extra chance to slay demons and survive the night. It was incredibly important to all of them.
But she didn't expose her sister's bluff.
The two sisters sat quietly by the veranda, neither speaking for a long while. The gentle wind sweeping through the courtyard carried the heavy, distinct scent of blooming wisteria, swirling the purple petals together with a strange, comforting sweetness.
"Sister."
After a while, the Butterfly Kakushi's voice dropped much lower than before. "Do you think Mr. Hikaru can really help us kill that Progenitor of Demons...?"
"Perhaps he can, perhaps he can't. Who really knows?"
The braided Hashira turned her eyes away without a second of hesitation and answered quite bluntly. "But I do think he might be the strangest, most terrifyingly distinguished guest in the entire bloody history of the Demon Slayer Corps."
"...Yeah."
The Butterfly Kakushi glanced back in the direction of the neighboring courtyard and deeply agreed with that assessment.
Although it had only been two short days since he arrived, the young girl was truly, deeply impressed by the sheer presence of that undead monster.
Shortly afterwards, the braided Hashira excused herself to rest.
The Butterfly Kakushi noted her sister's exhaustion in her heart and silently went back to turning the heavy pestle, grinding the herbs.
The wind in the courtyard blew stronger, causing the hanging wisteria spikes to sway gently back and forth. Two or three loose purple petals drifted down from the branches and fell softly onto the ground right next to the stone platform.
Then—the petals suddenly stopped moving.
They didn't continue to roll across the stone with the wind, acting exactly as if they had been gently pressed down flat by an invisible weight.
In the meantime, the shifting wind also carried more distinct sounds over from the neighboring courtyard.
The Butterfly Kakushi stared blankly at those two or three pinned petals for a long while. Listening to the faint sound of dry laughter drifting over the wall, she suddenly thought of those terrifying, scarlet demon eyes.
She thought of that tall, imposing figure who always seemed so cold and stern on the outside, but was actually surprisingly 'gentle' to the inanimate things around him.
And when she finally snapped back to her senses.
She looked down and found that the delicate medicinal herbs in her hand had already been completely ground into a fine, useless powder. She stared blankly at the ruined pile of powder, slowly reached down to touch the cold hilt of the Nichirin Blade resting at her waist, and let out another silent, heavy sigh.
She firmly decided that the next time she wanted to watch the excitement, she would make sure to keep a safe distance of at least two full courtyards away.
When making delicate medicine, one absolutely must not be distracted. She couldn't let this precious sword down. She had to work much harder.
But speaking of which...
"Breathing Style... could I possibly learn it too?"
Hearing the muffled conversation about breathing techniques in the neighboring courtyard, she thought about her own lack of talent. If it were before today, she would never have even entertained such a foolish thought. She was just a Kakushi. But now, feeling the comforting weight of the newly forged Nichirin Blade at her waist made a small, desperate desire sprout in her chest.
She really wanted to...
"You can try."
A cold, deadpan voice suddenly spoke from right above her.
The Butterfly Kakushi, who had just been distracted again, violently snapped back to reality. This time, she looked up and directly locked eyes with a pair of glowing, ghostly scarlet eyes hanging upside down from the veranda roof, appearing and disappearing like a terrifying phantom.
Then, she let out a piercing shriek of absolute fright.
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