As always, the sun rose from the east, and with its light, the darkness of night was gradually driven away.
Shinobu Kocho woke early. After washing up, she began her routine—carefully examining the condition of every boy and girl training on Mount Sagiri, paying special attention to the one practicing the Sun Breathing technique.
Fortunately, the boy's body had already begun to adapt to the intense heat generated by Sun Breathing.
As a physician, Shinobu could clearly sense the burning nature of this technique. It carried a power akin to sunlight itself—a force that would undoubtedly be especially effective against demons.
Though she had yet to witness it firsthand, she could easily imagine its impact.
If more swordsmen within the Demon Slayer Corps could master Sun Breathing… then perhaps the disadvantage they had endured against demons for centuries could finally be overturned.
And beyond that—
There was the Bright Red Nichirin Sword.
The Demon Slayer Mark.
The Transparent World.
If all of these could truly be realized within the Corps…
Then their overall strength would rise to a level almost beyond imagination.
Just thinking about it made Shinobu's heart stir with excitement.
On most days, after finishing her duties as a physician, she would quietly train on her own.
But today was different.
She found herself lingering in place, waiting—almost unconsciously—anticipating the arrival of someone.
And in that quiet anticipation, a trace of regret surfaced in her heart.
Perhaps… she had left too many bad impressions on him before.
Not long after, that familiar figure finally appeared.
A flicker of excitement rose within her, and before she realized it, she had already walked toward him.
Seeing Soma approach, Shinobu straightened slightly.
Soma gave her a brief nod before heading toward the boy she had just examined—the one training in Sun Breathing.
After asking the boy to demonstrate briefly, Soma observed in silence.
It was clear that the boy's training was progressing smoothly.
"It seems there are no issues," Soma concluded calmly.
Afterward, he returned to his quarters, picked up a brush and paper, and began recording the day's observations.
Shinobu followed behind him, wanting to say something—but found herself at a loss for words.
When he finished writing, Soma gathered the records from the past few days and went to find Sakonji Urokodaki.
"These are the records of the boy's Sun Breathing training," he said. "I've documented the entire process. If other trainers encounter someone capable of learning Sun Breathing, they can try using this method."
Urokodaki accepted the papers. After reading through them, he couldn't help but feel impressed.
"…Why didn't I think of this?" he muttered. "I should also start writing down my own training methods."
"Your approach has inspired me as well," Shinobu added quickly, finally finding an opening to join the conversation. "I should document my medical treatment methods too."
The three of them began discussing the idea further, even touching upon the shortcomings in the current system for training new Demon Slayers.
On this topic, Urokodaki had the most to say—and the deepest resentment.
Too many of his promising students had died on Mount Fujikasane.
Shinobu listened quietly, occasionally joining in. Though her expression remained composed as always, the cold rigidity she once carried had softened. At times, when the discussion turned to something promising, the corners of her lips would even lift slightly.
For someone like Shinobu—who was usually seen as distant and unapproachable—this was a rare sight.
…
Before long, a new proposal for training recruits in the Demon Slayer Corps was sent off to headquarters via a Kasugai crow.
Standing by the window, Urokodaki watched as the crow flapped its wings and disappeared into the distance. A faint smile appeared in his eyes.
Ever since he had retreated into seclusion on Mount Sagiri, sorrow and pain had followed him relentlessly. One after another, his students had perished during the Final Selection at Mount Fujikasane.
Each new year brought with it a quiet dread—the fear that he would lose yet another beloved disciple.
Until…
Soma arrived at Mount Sagiri.
And everything began to change.
First came the inheritance of Sun Breathing… and the legacy of Yoriichi Tsugikuni.
With his help, the last of his disciples, Makomo, finally passed the trial on Mount Fujikasane. Only then did the truth behind the repeated failures of his students over the years come fully to light.
And that was not all. Now, he had also come to understand concepts such as the "Bright Red Nichirin Sword," the "Demon Slayer Mark," and the "Transparent World."
Though his knowledge of them remained largely theoretical, to someone like him—who had long struggled against the limits of his own strength—it felt as though a shuttered window had suddenly been thrown open, letting in a rush of light.
On top of that, there was now a renewed approach to training and reforming the new generation of recruits.
Sakonji Urokodaki could already foresee it: in the years to come, the balance of power between the Demon Slayer Corps and the demons would be fundamentally transformed.
"Truly... an extraordinary person."
The thought rose unbidden in his mind, and for the first time in many years, he found himself offering such genuine praise to another.
Though his body had already grown old, this new generation made him feel, for the first time, a genuine hope that Muzan Kibutsuji could be killed.
Standing by the window, he looked outside.
The young trainees who had arrived not long ago were diligently honing their skills. His sole disciple, Makomo, was patiently guiding a young girl through her forms. Not far away, Tanjiro gripped his Nichirin Sword over and over again, as if attempting to awaken the power of the Bright Red Nichirin Sword through sheer will.
Urokodaki watched in silence.
Everything before him brimmed with vitality, with promise. And yet, in contrast, his own aging body felt like the setting sun—its light fading, destined soon to sink below the horizon.
Even as a former Hashira, even in retirement, there were still duties he could not abandon.
Training disciples was one part of it. Recording his insights and passing them on to other trainers was another. Urokodaki believed that in the future, the Demon Slayer Corps would grow far more effective in nurturing new recruits. In that regard, his own role was gradually diminishing.
For veterans like him, what mattered most now was something else entirely—
To carve out a new path forward for those who would come after.
"I never imagined… that this decaying body of mine would still have a purpose to serve."
Turning away from the window, Urokodaki walked deeper into the house and picked up his Nichirin Sword.
Since his retirement, this old companion of his had remained sheathed for far too long. His hand tightened around the hilt, though the strength in his aged body was no longer what it once had been.
"I'm not… that old yet."
He increased the force in his grip once more, closing his eyes as he guided the heat within his body into the blade.
Hiss.
Almost instantly, the blade began to surge in temperature.
Opening his eyes, Urokodaki quietly observed the Nichirin Sword now glowing red in his hand.
"So this is the 'Bright Red Nichirin Sword'…"
He could feel it—the heat radiating from the sword, like the sun itself.
Against demons, such power would be overwhelmingly effective, a force they could hardly withstand.
However…
"To maintain this state is far from ideal. Right now, nearly all my focus is spent sustaining the Bright Red Nichirin Sword. In actual combat, this could even reduce my overall effectiveness. Unless used at a specific moment—such as the instant of severing a demon's neck—this state was best treated as a finishing tool rather than a constant one."
He paused, considering.
"It seems the Demon Slayer Mark must come first. Only by awakening the Mark and greatly enhancing one's combat ability can the Bright Red Nichirin Sword be maintained as a constant state without hindering performance."
As for the Mark itself, now that he understood its principles, it was not nearly as unattainable for someone of his experience as one might imagine.
The true difficulty lay elsewhere.
Once the Mark was awakened, one's lifespan would inevitably be shortened—
Unless a way could be found to wield its power without paying that price.
However, Soma himself did not seem to know how to prevent the life-draining effects that came with awakening the Demon Slayer Mark.
Pouring himself a cup of sake, the old man let out a carefree chuckle. Under his breath, he murmured, "When one person awakens the Mark, it's as if they become a magnet… those around them begin to resonate, and the Mark appears in them as well."
If that were the case, then once a single individual awakened the Mark, wouldn't it lower the threshold for others to do the same?
A faint smile lingered on his lips as he slowly closed his eyes. His breathing grew rapid, his heartbeat quickening as his body temperature began to rise—climbing swiftly to levels the human body could scarcely endure, surpassing thirty-nine degrees.
As the heat intensified, every organ in his body cried out in protest. For someone as aged as he was, those worn and fragile organs sent out unmistakable warnings of danger.
And yet, his expression remained as calm and still as an ancient well, utterly undisturbed by the strain.
Then, at some point… it happened.
The old man stopped.
Once again, he gently gripped his Nichirin Sword. This time, he did not exert his full strength—yet the blade remained bright red almost effortlessly, as though that were its natural state.
Not only that, but every aspect of his physical ability had risen dramatically. Compared to his normal state, he felt several times stronger.
Slowly, he rose to his feet and walked toward the bronze mirror in the room.
Standing before it, Sakonji Urokodaki removed the tengu mask from his face, revealing his gentle features reflected in the dim surface.
And there—
Upon his forehead—
The Mark had appeared.
At the same time, he could feel it clearly: the quiet, undeniable draining of his life force.
In that moment, Urokodaki raised a hand and lightly touched the mark on his forehead, his voice low as he murmured to himself,
"So… this is the Demon Slayer Mark."
A faint breath escaped him.
"As expected… it is powerful."
...
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