"You are truly generous, my lord. To forge several dozen Nichirin Blades in a single stroke… I am certain the Master will be overjoyed when he hears this news." On the journey back, Chō was brimming with happiness. She, too, had received a Nichirin Blade, a gift from Shinji, granted with the tacit approval of the smiths of the Swordsmith Village, as recompense for guiding him here.
Even though that had simply been her assigned duty. Though she was only a Kakushi, a member of the rear support unit, in her heart, Chō had always yearned for a Nichirin Blade of her own.
She longed to step onto the front lines, to become a demon-slaying swordswoman. She simply lacked the ability. Beyond this, had Shinji not firmly refused, the smiths of the Swordsmith Village would have gladly knelt before him, begging him to stay and teach them his forging arts.
But Shinji knew his own limitations well. Setting aside his Affection System, in terms of pure smithing skill, he might not truly surpass these men who had spent their entire lives hammering blades by very much.
He had, naturally, declined. And he had left the blades he forged to the Demon Slayer Corps. He kept only the most essential, core blade… and a second blade, slightly inferior to the first.
In the days that followed, Shinji returned to the Demon Slayer Corps. He had just obtained his Nichirin Blade. He needed to familiarize himself with it. And then, begin its cultivation.
The Ubuyashiki Estate. The rear courtyard. Wisteria cascaded from the trellis overhead, forming a natural curtain of flowers. The pale violet clusters swayed gently in the morning light.
Shinji sat cross-legged upon a stone platform in the garden. Across his knees lay a blade. A Nichirin Blade. The sheath was deep crimson. The hilt was wrapped in white silk cord. Embedded in the pommel was a piece of scarlet ore the size of a thumb.
The color of the blade was exceptionally unique, not the silver-white of ordinary steel, nor the pitch-black of dark iron, but a faint orange luster, pale as the first light of dawn.
That was the hue formed when the power of sunlight, absorbed over years of relentless exposure by the scarlet iron sand and scarlet ore, seeped into the metal's very structure.
The Nichirin Blade, also called the Color-Changing Blade. The signature weapon of the Demon Slayer Corps. Yet this one had been forged by Shinji's own hands. Its raw materials were scarlet iron sand and scarlet ore, gathered from the sun-drenched mountain.
The ore, exposed to sunlight all year round, had absorbed its energy, and through a unique smithing process, that energy was tempered into the blade's edge.
Its slashes carried the properties of sunlight itself. It was the only known weapon that, even in the hands of an ordinary swordsman, could completely sever the immortality of demons. And its color would shift according to the nature of its wielder.
Thus, the System panel had already flickered to life.
[Nichirin Blade (Unattuned)]
[Quality: Demi-Demon Artifact]
[Description: A demon-slaying blade forged from scarlet iron sand and scarlet ore. The blade contains the power of sunlight accumulated over countless years. Due to its materials, it surpasses artifacts of ordinary quality, yet it lacks a sword-soul and does not belong to the class of demon artifacts.]
[Current Affection: 15 (Fondness)]
Because it had been forged from ore cultivated by Shinji's own Affection, it naturally carried a baseline favorability toward him. It was, unmistakably, a demi-demon artifact.
This was only to be expected. The raw materials of the Nichirin Blade were extraordinarily special. The scarlet ore had absorbed centuries of sunlight, nurturing a dense, potent spirituality.
Add to that Shinji's unique "forging technique", which had preserved nearly all of that energy, and in its very essence, it was on the verge of becoming a true yōkai. It lacked only a final step. But it already possessed properties no mundane blade could claim.
Thus, it was a natural demi-demon artifact. And a demon artifact that could, at any moment, undergo its final metamorphosis. This was something no other Nichirin Blade possessed, even the ones he had gifted away were the same.
Shinji laid his palm over the sheath and began infusing it with his yōki. Hum. The blade vibrated once. A tiny tremor, like the reaction of someone touched in their sleep. Then it stilled.
After all, it was only a demi-demon artifact. A Nichirin Blade's response to yōki was far less sensitive than that of a true demon artifact. It had been born to slay demons.
The power of sunlight contained within it did not reject yōki, but neither did it align with it. Even with a base level of Affection, cultivating this blade would not be simple. But neither would it be difficult.
Because Shinji possessed the Blood-Fire Transformation. Fire belonged to the Yang element. Though the yōkai-fire flowing through his veins originated from Tōtōsai's forge and was, in essence, a product of impure energies, the fundamental nature of fire was universal.
Temperature. Light. Combustion. These things shared a resonance with the power of sunlight within the Nichirin Blade. All he needed to do was find that resonance point.
As expected, the System panel flickered.
[Nichirin Blade: Affection +1]
[Current Affection: 16 (Aware)]
It had begun. He was growing more and more practiced at this. Shinji couldn't help but feel he was straying further and further down the path of a "player of hearts". only with artifacts.
At the same time, on the other side of the rear courtyard, Tsugikuni Yoriichi sat upon the wooden floor of the veranda, his bare feet brushing the edge of the steps. Across his knees also lay a blade.
Not the hatchet he habitually used to chop firewood. A Nichirin Blade. Though Yoriichi had not yet formally entered the ranks of the Demon Slayer Corps, by principle, he should not yet possess a Nichirin Blade. But principle, in this case, bowed to him.
This blade, naturally, was a gift from Shinji. It was the second blade Shinji had forged, the one slightly inferior to his own. Yet "inferior" was only relative. It still far surpassed any ordinary Nichirin Blade.
It remained a mundane blade, but it could perfectly bear Tsugikuni Yoriichi's Will. Ubuyashiki, as before, had tacitly approved. The Master of the Demon Slayer Corps, gentle as he seemed, was in truth exceedingly decisive. Decisive to the point of near ruthlessness.
This blade. The current situation. And the fact that Yoriichi's wife, Uta, had already been settled into a quiet room within the estate's inner quarters, where the Ubuyashiki household's maidservants were tending to her.
The midwife had been arranged. Everything was prepared for the imminent birth. The Demon Slayer Corps headquarters had physicians, and among the families of other Corps members residing there was an experienced midwife.
Uta was safe. The child was safe. For this, Tsugikuni Yoriichi was deeply grateful to Shinji, and, by extension, to the Demon Slayer Corps. Knowing now that this organization existed to destroy those man-eating demons, he felt he, too, should lend his strength to their cause.
The red-haired young man lifted his head. His deep crimson eyes watched the wisteria petals dancing through the courtyard. Then he closed his eyes. Within his Transparent World, every current of air throughout the entire estate was visible.
Every path the wind took. Every breathing rhythm of every person. The growth of every wisteria vine. But the Transparent World never held only the present. It also held the past. His thoughts drifted back to that night. He was thinking. Thinking of those demons.
Thinking of the old man he had subdued, then let go. That chāng. That human controlled by a demon. The existence of such a thing proved that demons had intelligence. Organization. Purpose.
He was also thinking of the demon that Shinji had obliterated with a single slash. When he had reached the scene, all he had seen was a blackened chasm and the lingering stench in the air.
That thing had been destroyed too cleanly, so cleanly it reminded him of the fragmented human anatomical scrolls he had seen as a child in the Tsugikuni family's swordsmanship dojo. Those creatures feared the sun. This was the information the swordsmen of the Demon Slayer Corps had told him.
Demons could only move at night. The moment they were touched by sunlight, they would crumble into ash. That was why the Corps wielded blades imbued with the sun's power.
Yoriichi lowered his head and looked at the blade in his own hands. A Nichirin Blade. A blade forged from ore that could absorb sunlight. Against those demons, it was indeed effective. But it was still clearly not enough.
Relying solely on a blade that carried the sun's power was still too uncertain. According to what Sir Shinji and Sir Rengoku had said, the casualty rate among the Corps' swordsmen remained devastatingly high.
What if… he used what he was best at, his breathing, to emulate the sun? To make himself become the sun? With such a blade, combined with the rhythm of sun-like breathing, at the moment of the slash, to incinerate the oxygen in his lungs to its absolute limit, to wring his body's potential to its breaking point, would the strike that followed truly carry the temperature of the sun?
The thought took shape in his mind, growing sharper, clearer. He closed his eyes. He adjusted his breath. But it was different from the primal form of the Breathing Technique he had used before.
Deeper.
Slower.
Longer.
On the inhale, pressing the air into the deepest recesses of his lungs. On the exhale, expelling every last trace of waste. The rhythm was perfectly even. The cadence constant. Like ocean waves beating against the shore. Like the wind blowing through a mountain valley.
This was a skill he had grasped naturally since childhood. He did not know that it could be called a Breathing Technique. He did not know that he was the only person in this world who could breathe in this way. He only knew that when he breathed like this, his body grew lighter. His vision grew sharper. His hands grew steadier. His strength swelled beyond its ordinary bounds.
Understanding dawned in his heart. He rose abruptly to his feet and lifted the blade in his hand. The steel was dull and lusterless beneath the morning light. But the breath of the man holding it, changed. Deep. Dense and continuous.
The same as before, yet carrying a rhythm of breathing utterly distinct from anything that had come before. When he inhaled, his chest seemed to take in the entire sky.
When he exhaled, heat seeped from his pores, forming a layer of heat-haze around his body, nearly visible to the naked eye. He slowly raised the blade. And then brought it down.
A single slash. Very slow. Very light. But the air that stroke passed through, charred. It truly charred.
Along the blade's arc, the air was flash-heated to an impossibly high temperature in an instant, leaving a brief, blazing orange-red afterimage. Like the lingering ghost of sunlight. Not a mere visual effect. Not an illusion.
Because that single slash from Tsugikuni Yoriichi had faintly stirred the convergence of energy between heaven and earth. In this merged world, Breathing Techniques truly carried power.
From the far end of the corridor came a sharp gasp. Rengoku Jinjūrō stood there, though no one knew when he had arrived. His crow mask had been removed.
Beneath his thick brows, his eyes were stretched wide. "Sir Tsugikuni… what… is this?" Though the man before him was, by all outward appearances, nothing more than a woodcutter, Rengoku Jinjūrō had witnessed his strength. His respect was profound.
Yoriichi turned to look at him. He paused, as though searching for the right words. In the end, he simply gave it a name. "Breathing Technique."
Simple. Direct.
"Using the breath as a foundation to amplify everything the body is capable of. What I just used… perhaps it can be called the Breath of the Sun. A breathing method that emulates the shifting light of the sun."
Rengoku Jinjūrō's mouth opened, then closed. He was not yet a Hashira, but he was already one of the de facto strongest members of the current Demon Slayer Corps.
And yet even he had never seen this. The ability to amplify one's own strength through breath alone. The samurai, the schools of swordsmen, at most, they used breath to exchange air, to build spirit, to maintain the rhythm of combat.
His hand, so accustomed to gripping a Nichirin Blade, was now trembling faintly. Because he sensed it. This could very well be the method that would allow humanity to directly match the strength of demons, and, if necessary, yōkai. Not through encirclement. Not through traps. Not through mass sacrifice. But through the power of one's own body alone.
"Can you… teach me?" The words escaped him before he knew it.
Yoriichi looked at him. "Yes." No hesitation. Nothing held back.
He thought of it, and he did it. He felt this was only right. A return for the help the Demon Slayer Corps had given him. He reversed the Nichirin Blade and extended the hilt toward Rengoku Jinjūrō.
"Begin with the breath. Take a deep breath. Fill every corner of your chest with air. Then exhale slowly. As you exhale, feel the blood within your body. Let it flow. Let it accelerate. Let it grow hot. Remember that sensation. That is the starting point."
Rengoku Jinjūrō took the blade. He drew a deep breath. He tried. And then broke into violent, hacking coughs. He failed. Unsurprisingly. But his eyes, they blazed even brighter. So bright it was almost impossible to look at them directly. He had felt it. Truly felt it.
And throughout all of this, on the stone platform across the courtyard, Shinji, even as he continued channeling his yōki into cultivating the Nichirin Blade, had been watching from the corner of his eye.
His crimson demon gaze narrowed faintly. He was observing. And he was learning. That Tsugikuni Yoriichi had created the Breath of the Sun just like that, Shinji was not surprised.
Even setting aside the original Demon Slayer storyline, simply from everything he had witnessed so far, Shinji had already formed a fairly clear understanding of Tsugikuni Yoriichi's existence.
He was strong. Innately strong. Yet also acquired strength. Yoriichi's Will… was nothingness. No desire. No demand. No self. And beyond that, boundless growth.
The upper limit of his strength was determined by his environment. And even more, by the "push" of those around him. This was why, though he had lived in this merged world all along, he had never been excessively powerful.
His surroundings had never demanded it. Now, his environment had changed. What was meant to come, would naturally arrive.
As for the Breathing Techniques, just as with the Nichirin Blades, Shinji held a certain interest. As he had noted before, breathing methods were common to every world, every discipline.
Shinji had seen no shortage of them. Even his lover, the woman many called the greatest miko of the Warring States, Kikyō, could likewise channel power through her breathing. Only, what Kikyō breathed was the higher-level pure energy. Through it, she could mobilize her reiryoku, projecting it beyond her physical body.
The Breathing Techniques, on the other hand, circulated the energy between the pure and the impure. The energy of living beings. Its purity was lesser. The gulf between the two was evident. They were hardly compatible. But that did not mean Yoriichi's Breathing Techniques were without value.
If one fell short of the best, one still surpassed the rest. The Breathing Techniques could not compare to what Kikyō wielded, but what lay in between were still the teeming masses of humanity.
The best among the ordinary. An ability that could momentarily amplify the physical form, an ability that could be grasped through human effort, it could be regarded as a form of demonic physical transformation.
A "transformation of mortals." Shinji simply could not be certain whether the Breathing Techniques would work on himself. But that did not stop him from trying.
Compared to the pure reiryoku that Kikyō wielded, which he currently had no means of touching at all, this was far more within the realm of possibility.
And so, in that moment, Tsugikuni Yoriichi's every movement. Every shift in the rhythm of his breath. The amplitude and frequency of his chest's expansion. The flow of air within his body.
All of it was captured by his demon eyes, enhanced by the Keen-Eye Change.
Once. He only needed to watch it once. He had already memorized the foundations of the Breath of the Sun.