What is cognition?
Cognition is the process by which humans, through perception, memory, and thought, acquire, process, and apply information. It includes our capacity to understand and adapt to the objective world.
In short: everything seen, heard, thought, felt, and experienced, woven into a complete system.
Roy had watched Demon Slayer in his previous life, slipped into its characters, shared their joys, their grief, their resentments, their rage. So he left a deep footprint in his own cognitive world.
Pensive, he rolled up from the snow. A small cloth pouch slipped from his chest, scattering a few candies. He remembered that today was the one-month celebration for his youngest sister, Kamado Hanako.
Because of his intervention, Tanjiro Kamado was no longer the eldest son in the family. The youngest child from the original story, Rokuta, had not yet been born. In other words... the plot was still two or three years away.
Not only was his father, Tanjuro Kamado, alive, but even the white-haired grandmother who often hugged Tanjiro to watch the stars was still here.
Curious indeed. In reality Roy was the Zoldyck family's eldest son. In his cognitive world he was still the Kamado family's eldest son. Perhaps that "fit" was why he could push open the Demon Slayer door.
Sensing the connection, Roy bent down, picked up the candies one by one, then checked his body state.
First, Nen...
He tried to commune with the aura within, guiding it to the tip of his right index finger. A milky halo quivered there—faint, not striking against the white snow, yet undeniably present.
He let out a quiet breath.
This world, like Hunter × Hunter's, was no peaceful place. Man-eating demons prowled here. Having or not having Nen mattered greatly before he learned a Breathing Style and obtained a Nichirin blade.
Next, assassination arts.
"Dark Step," "Limb Bend," and "Serpentine Life"...
"Dark Step": the Zoldyck clan's inherited assassination footwork, built on four keys—light, drifting, eerie, illusory.
In motion, light as a swallow; in strangeness, dreamlike. Roy set a foot down and floated like a ghost. East, then west, his figure threading the old forest, his trail impossible to read, and—without leaving a single footprint in the snow. This... instantly stunned a certain younger brother who had braved the dark out of worry for his big brother.
Today was Hanako's one-month celebration. Their father, Tanjuro, had sent the eldest brother, Eiichiro, down the mountain to buy supplies. Dusk neared, and he still hadn't returned. Kie, the mother of Eiichiro and Tanjiro, dispatched keen-nosed Tanjiro to look for him.
He did find him. Then he froze.
The simple, straightforward boy wore a thick black-and-green checkered coat with a light-purple scarf at his neck. He stood blankly in the swirling snow. Those pretty amber eyes reflected Roy's flitting, ghostly silhouette. His mouth hung open. The cry of "big brother" stuck in his throat.
In his heart a line repeated—Was this... still his brother Eiichiro?
Yes. One hundred percent Eiichiro.
Eyes can lie, but scents do not. Tanjiro's nostrils flared; the smell confirmed Roy. He quietly crouched behind a big tree, only his head peeking out.
Having just drilled Dark Step and reacquainted himself with the body, Roy didn't rest. He shifted straight into "Limb Bend."
This assassination art is, in essence, an advanced application of Dark Step.
Compared to Dark Step, it adds a layer of misdirection for the opponent.
Roy drew a deep breath and stepped again. From where he stood, an instant ring of afterimages fanned out.
Killua Zoldyck had used this move against Isaac Netero on the airship during the ball test with Gon Freecss—only Netero's level was far too high, well beyond what a rookie without Nen could touch.
But that was the strongest human, Netero—not a still-green Tanjiro.
Seeing this, Tanjiro's eyes went wide again. He dumbly counted on his fingers, trying to figure out how many big brothers there were... when a sharp "ssht" split the air—
A blade-like hand strike slotted past his ear and stabbed into the trunk he was using for cover!
"Serpentine Life": hone the hand into a blade. Nothing resists it. At finesse it can pierce rock; at mastery, refined steel; at perfection, sever Nen-imbued tools.
Roy had seen Silva Zoldyck cleave a fine katana in one hand-chop with his own eyes.
For now he only had the rudiments—three-tenths into the wood was his limit. More would take time to grind in... unlike killing-intent sense, which one can glean a trace of by long exposure.
Yes—at the moment Tanjiro found him, Roy had already sensed Tanjiro.
He drew his hand from the punctured trunk, smiled at this brother both familiar and new, and said, "Mother sent you to find me, didn't she? Sorry, I dozed off and made you worry."
Tanjiro looked at Roy's face, then at his right hand. His body was breathing, but his spirit seemed not yet back. He nodded dumbly, then shook his head like a rattle drum.
Roy chuckled and ruffled his hair. "A lot of questions?"
Tanjiro shook his head, then nodded.
Roy's smile deepened.
Gently he said, "Today is Hanako's one-month celebration. Let's celebrate her first, then talk, all right?"
Tanjiro nodded hard.
Roy patted his shoulder. No more words. He flicked his toe, caught the hoe in his hand, bent to shoulder the basket, and strolled toward home.
Tanjiro followed step for step, head buzzing, until the moon climbed the treetops and stretched their shadows long—
Only then did they stop.
Through the wind and snow, a cluster of familiar cabins came into view.
From the east-facing one, thin smoke curled. Faintly, children's laughter and adults' coughing could be heard. Add a few barks and meows and it would be a warm mountain village scene.
"Only... this world truly has demons. In two or three years this place will be gone..."
Roy murmured.
Tanjiro looked up, puzzled. "Demons?"
Clearly, big brother didn't want to explain more. With one more glance, he set off again toward home.
Tanjiro blinked, tightened the scarf at his neck, and hurried after.
Hearing movement, the people inside—young and old—peeked out. Seeing Roy and Tanjiro, the children cheered.
There was Nezuko, Takeo, Shigeru, and the smallest, Hanako, still swaddled in the arms of a white-haired grandmother.
"Brother Eiichiro, you're back!"
"Mm. I'm back."
Roy answered with a smile, his gaze meeting the man seated at the veranda's corner.
The man coughed a few times, hands arranging a set of Japanese ceremonial clothes. When he noticed Roy looking, he returned a gentle smile of his own.