Chapter 3: Assassin's Training × Brothers' First Meeting
What is cognition?
Cognition is the process by which humans, through perception, memory, and thought, acquire, process, and apply information. It encompasses our understanding of the external world and our ability to adapt to it.
In short: everything one sees, hears, thinks, and experiences comes together to form a complete system.
Roy had watched Demon Slayer in his previous life. He had empathized with its characters, shared in their joys, their sorrows, their regrets, and their rage. That was why, within his world of cognition, a deep footprint of the Kamado family had remained.
He mulled this over as he sat up in the snow. A small cloth pouch slipped from his chest, spilling out several pieces of candy. Only then did he remember—today was his younger sister Nezuko's one-month celebration.
But with his intervention, Tanjiro was no longer the eldest son of the family. The child who, in the original story, would later be born last—Rokuta—had yet to even exist. Which meant the events of the story were still two or three years away.
Not only was his father, Tanjuro Kamado, still alive, but so was his grandmother—the white-haired woman who often held Tanjiro close while gazing at the stars.
It was strange. In reality, Roy was the eldest son of the Zoldyck family. Yet here, in his world of cognition, he was again the eldest son—this time of the Kamado family. Perhaps it was this "fit" that had allowed him to open the Demon Slayer door.
Roy sensed the connection. He bent down, picked up the candies one by one, and tucked them back into the pouch. Then, he began checking the state of his body.
First—Nen.
He tried channeling the aura within him, gathering it toward his right index finger. A faint milky glow flickered to life. It was weak, and barely noticeable against the white of the snow, but it was real.
Roy exhaled in relief.
After all, this world—like that of Hunter × Hunter—was not safe. It was a land prowled by man-eating demons. Without Nen, and before mastering Breathing Techniques or wielding a Nichirin blade, survival would be impossible.
Next—assassination arts.
Silent Step. Limb Bend. Serpent Flow.
Silent Step: a footwork passed down through generations of the Zoldyck family. Its essence lay in four qualities—light, drifting, elusive, and illusory.
Roy stepped forward lightly. His movement was as airy as a phantom's. At times he shifted east, at times west, his form weaving through the ancient forest. His figure flickered like a ghost, yet on the snowy ground beneath him, not a single footprint was left behind.
This… was enough to leave one young boy utterly stunned.
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Today was Nezuko's full moon festival. Their father, Tanjuro, had sent the eldest son, Sumihiko (Roy), down the mountain to buy supplies. But as evening neared and he had not returned, their mother, Kie, grew anxious. She sent Tanjiro—her sharp-nosed son—out to find him.
And so, Tanjiro had found his older brother… but what he saw left him speechless.
The innocent boy, bundled in a thick black-and-green checkered coat, a pale violet scarf around his neck, stood dumbstruck in the falling snow. His amber eyes reflected the ghostly figure darting through the forest—his brother moving with the grace of a phantom.
His lips parted, but the word "Onii-chan" caught in his throat.
In his heart, one thought repeated again and again:
Is this… really my big brother Sumihiko?
Yes—there was no doubt. One hundred percent, it was his brother.
Eyes could deceive, but scent never lied. Tanjiro flared his nostrils, confirming the smell was unmistakably Roy's. Quietly, he crept behind a tree, peeking out with just his head.
Meanwhile, Roy, having practiced Silent Step and grown familiar with this body, did not stop. Without resting, he moved directly into the next technique: Limb Bend.
This assassination skill was, in essence, an advanced extension of Silent Step.
Compared to Silent Step, this next technique carried an added layer of deception.
Roy drew in a deep breath and stepped forward. From his starting point, a ring of afterimages burst outward in an instant.
This was the very move Killua had once displayed during the Hunter Exam, when he and Gon tried to snatch a ball from Netero aboard the blimp. Of course, against someone of Netero's level, a child with no Nen was little more than a joke.
But Tanjiro was not Netero. He was still green, untested.
The moment Tanjiro witnessed the illusionary figures, his eyes went wide. He began fumbling with his fingers, trying to count just how many brothers stood before him—
"Shhk—!"
A sharp sound cut the air. A hand-chop, keen as a blade, drove straight into the tree where Tanjiro was hiding, burying itself inches from his ear.
This was Serpent Flow: forging the hand into a blade, able to pierce wood and stone. At higher mastery, it could pierce steel. At perfection, it could sever even weapons infused with Nen.
Roy had once witnessed Silva himself cleave a masterwork katana in half with a single hand-chop.
His own skill was still at the rudimentary stage. For now, cutting several inches deep into wood was his limit. To go further would require years of grinding practice—unlike his instinctive sense for bloodlust, which he had partially absorbed just by growing up in the Zoldyck family.
Yes, the very moment Tanjiro had found him… Roy had already sensed Tanjiro's presence.
Pulling his hand from the split trunk, Roy turned and smiled warmly at this familiar yet new little brother.
"Mother sent you to look for me, didn't she? Sorry—I fell asleep earlier. Must have worried you."
Tanjiro looked at his face, then at his right hand. His brother was breathing, alive, but his mind still seemed somewhere else. He nodded dumbly, then shook his head so hard it looked like a bobbing toy.
Roy chuckled at the sight, reaching out to ruffle his hair.
"Got a lot of questions, don't you?"
Tanjiro shook his head—then quickly nodded.
Roy's smile deepened.
"Today is Nezuko's full-month celebration. Let's go celebrate with her first. We'll talk after."
Tanjiro nodded fiercely.
Roy clapped him on the shoulder, then bent down to scoop up the hoe with the tip of his foot. Grabbing the tool, he slung the basket of coal onto his back and began walking home at an easy pace.
Tanjiro followed closely behind, his head buzzing, trailing in silence until the moon climbed high, casting their two shadows long across the snow.
At last, through the swirling flurries, the familiar outlines of their little wooden houses came into view.
From the easternmost home rose a thin plume of smoke. Inside came the faint laughter of children and the cough of an adult. Add a few barking dogs and mewling cats, and it was a perfect, idyllic mountain scene.
"…It's a shame," Roy whispered under his breath, "this world truly does have demons. In just a few years, all of this… will be gone."
Tanjiro tilted his head, puzzled.
"Demons?"
But his elder brother clearly had no intention of explaining further. With one more glance, Roy stepped forward again, heading straight for home.
Tanjiro hesitated, tugged his scarf tighter, and hurried after him.
Inside, the noise had stirred the household. One by one, figures peeked out. The moment they saw Roy and Tanjiro, the children erupted into cheerful shouts.
There was Nezuko, there was Takeo, there was Shigeru, and even the youngest—Hanako—cradled in the arms of their white-haired grandmother.
"Niisan, you're back!"
"…Yeah," Roy replied with a gentle smile, "I'm back."
His eyes drifted to the veranda, where a man sat coughing lightly, his hands arranging a traditional ceremonial robe. Tanjuro Kamado met his gaze and returned it with a warm, knowing smile.