When it came to teaching the Kochō sisters, Yōsuke adopted a different approach.
After all, the lives of humans were not like those of demons. For the likes of Hakuji and Gyūtarō, he could afford a "hands-off" method of letting them grow on their own.
But for the Kochō sisters, that was impossible. A human's prime years for learning were limited to just a handful, and how much knowledge they absorbed during that window would determine their future potential.
At this moment, Kochō Kanae was only eleven, and her younger sister Shinobu just nine. They were at the very peak of their learning years. Yōsuke had to personally guide them while their minds and bodies were still in that golden period.
Thus, in order to properly train the sisters, Yōsuke abandoned his wandering life of hardship and settled down in a small village.
Since he had agreed to take them on, he would bear that responsibility fully.
Inside the house—
"Breathing Techniques," Yōsuke explained, "are a skill devised by human demon slayers to counter demons whose physical abilities far exceed their own. Their primary function is to strengthen the heart and lungs, allowing the body to take in an immense amount of oxygen in a short period. This, in turn, grants a drastic boost to physical ability, enabling a human to temporarily fight on par with demons."
Kanae and Shinobu pulled out notebooks and began writing intently.
Puzzled, Yōsuke asked, "What are you two writing down?"
"I feel that what Master is teaching us is very profound," Kanae replied. "So I want to record it carefully and study it over and over."
"You don't need to take notes," Yōsuke said, shaking his head. "For now, I'm only introducing what Breathing is. Instead of recording words, it's far more important that your bodies remember it."
Their earnestness nearly left Yōsuke at a loss. He thought back to when he had whimsically tried to teach Hakuji and Gyūtarō.
The less said about that disaster, the better.
Since then, he had adopted the "hands-off" approach with them.
"You'll begin with the most basic breathing exercises. Once you can fully control your breathing, you'll have taken your first step. At that time, I'll begin teaching you Water Breathing."
With their master's approval, the sisters became highly motivated, throwing themselves into breathing practice with all their energy.
That night, Yōsuke stepped outside. In his mind, he had already formed a plan for their training.
In the future, Kanae would derive Flower Breathing from Water Breathing, while Shinobu would in turn develop Insect Breathing from Flower Breathing. His task now was simply to guide them steadily through the foundations of Water Breathing.
But for demon slayers, one thing was indispensable: a Nichirin Blade.
His own blade had been abandoned on the battlefield during the assault on Muzan Kibutsuji. Now, he would have to prepare two new Nichirin Blades for the sisters, so they could train in sword forms alongside breathing.
In the pitch-black night sky, a crow with scarlet eyes swooped down.
The demon crow alighted on Yōsuke's shoulder. Closing his eyes, Yōsuke read through its memories.
The corner of his lips curved upward.
"So… it's been found?" he murmured.
With a beat of its wings, the crow departed. Unfurling the blood-red wings on his back, Yōsuke followed it, descending into a forest.
There, a squad of Demon Slayers was locked in a desperate battle against a demon.
Breathing was the most basic skill required of a slayer. But the sword forms that paired with Breathing were not something every member could master.
Though the techniques of all Breathing Styles were freely accessible, most ordinary slayers could spend their entire lives mastering only one.
Those with exceptional talent, however, were chosen as the "Tsuguko" of a Hashira, receiving direct instruction and being groomed as the next generation of Pillars.
Observing silently, Yōsuke noted how much stronger the Corps had grown compared to centuries ago, in the era of Ubuyashiki Kagaya.
Back then, Breathing itself had only just begun to spread. Few even knew of it, let alone mastered it.
But now, mastering Breathing was the minimum requirement to become an active slayer. Those unable to do so could only serve in support divisions.
Even so, the demons prowling the land now were far more dangerous than in ages past. Muzan, in hiding, had created demons of greater strength than before.
The one before him now was proof—holding its own against an entire squad, even toying with them.
The battle was nearing its end. The demon, losing patience, prepared to slaughter the slayers.
With a heavy beat of his wings, Yōsuke descended from the sky, his landing cracking the earth beneath his feet.
He unleashed his full aura as the Demon King.
The slayers froze, their eyes wide in despair.
"A demon… of this magnitude?"
Even the demon they had been fighting stood rooted in terror, cowed by Yōsuke's overwhelming presence.
Turning away from it, Yōsuke strode toward the squad. Their hands shook uncontrollably on their Nichirin blades.
As he neared the two closest slayers, they couldn't even muster the courage to swing their swords. They stared blankly at him, paralyzed.
Yōsuke reached out and plucked their Nichirin blades from their hands. The two collapsed to the ground, minds blank, breath forgotten, sweat streaming down their faces.
He offered no explanation for their fear, only spoke softly:
"As payment, I will slay the demon for you."
Before they could even register his words, Yōsuke vanished, reappearing instantly behind the demon.
The creature clutched its severed neck in disbelief, staring at him with wide eyes.
Yōsuke flicked the blood from the Nichirin blade in his hand.
"Are we not of the same kind? Then why… why kill me?" the demon thought, before its body crumbled into ash and scattered.
Having obtained the blades he needed, Yōsuke spread his wings once more and vanished into the night sky.
The Demon Slayers gasped for breath, wondering if it had all been a dream—if not for the absence of the demon they had been fighting.
They reported the encounter and the demon's slaying to Ubuyashiki Nichiya.
Nichiya was unsurprised. In fact, he guessed the reason Yōsuke had taken two Nichirin blades—and was quietly delighted.
Opening a lacquered box, he revealed a blade riddled with chips along its edge.
It was the very Nichirin blade Yōsuke had once abandoned on the battlefield.
"It seems," Nichiya said with a gentle smile, "that our Ubuyashiki ancestors truly did find someone worthy to inherit the will of the Breathing Styles."
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