(Brain optional, but not required)
...
During the Keian era (circa 1648–1652), as the sun set, demons devoured humans, and fear gripped the land. The Ubuyashiki family, determined to punish Muzan Kibutsuji for his atrocities, founded the Demon Slayer Corps with the ultimate goal of defeating him.
In the Sengoku period, the successive pharmacist Tamayo turned into a demon, and the Tsugikuni brothers rose to prominence—dark currents stirred among the people. In the end, the Sun Breathing lineage survived only through the Kamado line. The Demon Slayer Corps continued its mission, moving through villages to hunt demons.
Meiji Year 27—18 years before the Taisho era tragedy that would wipe out Tanjiro's family at Muzan's hands!
On the outskirts of Kazahana Village...
The grand Kanroji estate sprawled luxuriously, built against the northern mountain with wings folding westward in the style of ancient Tang Dynasty Chinese gardens. Every corner radiated refined elegance—a clear sign of great wealth.
Inside one of the rooms, a graceful and gentle woman exuded maternal warmth. She gazed tenderly at the dazed infant in her arms and smiled softly. "Kaede-rin-kun, where did you find this child?"
Unusually, the baby's eyes held an awareness far beyond his age.
This was no ordinary infant—it was Yi Ren, freshly transmigrated.
Back home, he'd been happily watching Demon Slayer when Mitsuri Kanroji, the Love Hashira, suddenly turned, smiled sweetly, and called out "Onii-chan!" Before he could react, a flash of white light engulfed everything.
When Yi Ren opened his eyes again, he lay in a dense bamboo grove, staring up at swaying stalks and the blue sky. Seeing his tiny, helpless hands, he let out a shocked wail—pure baby cries!
The empty grove filled him with despair. Time passed—he wasn't sure how long.
Just as he thought he'd starve in the wilderness, a man in samurai attire approached from afar. Yi Ren tried to cry for help, but hunger overtook him, and he blacked out.
When he awoke, a kind-faced couple watched him with gentle concern. From their conversation, he learned the man was Kanroji Kaede-rin, head of the Kanroji family, and the woman was Harada Yuri, his wife.
Kaede-rin carried himself with upright poise and warm eyes. He looked at the swaddled Yi Ren and asked softly, "Yuri, shall we adopt him? I found him in the bamboo grove—he looked so pitiful."
"Yes... If we have a daughter later, he can protect her. If a son, they'll be playmates."
Harada Yuri stroked her slightly rounded belly, radiating motherly glow as she gazed at Yi Ren.
Kaede-rin nodded with a smile. "He seems healthy—a boy. Let's raise him as our own."
"Mm! Kaede-rin-kun!"
And so, in a complete daze, Yi Ren was adopted by the Kanroji family—in an entirely different era!
Staring at his immobile infant body, he felt utterly lifeless. Just as he wondered if he'd transmigrated to ancient Japan...
A majestic yet calm voice echoed in his mind, inspiring awe across time and space.
[My lord, the wheels of your fate have begun to turn. The future of Demon Slayer is yours to write. Remember—the power of spacetime is limitless...]
"Future? Demon Slayer?! Who... who are you? Why am I here?!"
Yi Ren fired off questions, heart racing in the unfamiliar world.
But the voice never returned—only faint ethereal echoes remained.
Calming himself, he realized: this wasn't an ordinary world. It was the Demon Slayer world!
Surprisingly, he felt no panic—only quiet excitement. Transmigration without the usual truck impact? Nice. A break from his monotonous old life, a chance for adventure... and maybe some close moments with his waifu Mitsuri—and the other girls.
But when exactly was he?
Recalling the couple's names—Kanroji—he instantly thought of the adorable Mitsuri Kanroji.
Wait... did Mitsuri really pull me here with that glance?!
Remembering her cute expression right before the light, he chuckled inwardly. If he was truly in her family, protecting the girl who always wanted to be protected sounded perfect.
As his thoughts wandered, glowing ancient text appeared in his mind, accompanied by explanations:
[Sword Dao Physique: Absorb and refine the essence of all Breathing Styles to strengthen the body. Basic Swordsmanship: Encompasses the fundamentals of all sword techniques. Markings (Locked), Breathing Style (Not Awakened)]
The text dissolved into streams of light that merged into his body.
It felt innate—like skills he was born with, not a typical golden finger.
He could observe and fuse the core of any Breathing Style, while the basic swordsmanship covered nearly every form.
Eager to test it, he sighed—trapped in an infant body, he'd have to wait months just to walk.
For now... all he could do was stare at that protruding thing. Great.
...
Months flew by.
In the Kanroji courtyard, a black-haired, black-eyed toddler wobbled to his feet. It was Yi Ren, finally taking his first steps amid a circle of nursemaids.
(And no, the many nursemaids weren't because he was addicted—it was pure hunger. Totally. No excuses!!)
His milestone instantly drew attention.
"So cute!"
"Look at him go!"
"Should we go pinch those cheeks?"
The nursemaids beamed with auntie smiles, ready to pounce.
Then the couple arrived—Harada Yuri cradling a newborn baby girl, gentle and elegant as always. Kaede-rin stood beside her, imposing yet smiling softly.
"Yuri, look—Yi Ren's walking already. Wonder when our Mitsuri will."
Yuri shot him a playful glare, caressing the infant girl's cheek. "She's only a few days old, and you're already talking nonsense. By the way, Kaede-rin-kun, why name him Yi Ren?"
"There's an old Chinese poem: 'The one I long for, wanders freely here.' It means a wise person finally arrives and lives in joy—like this little guy. I hope he'll become our family's wise one."
Kaede-rin chuckled, then frowned slightly at Yi Ren. "Though his appetite is huge. Without all these nursemaids, Mitsuri might go hungry."
"Hmph! Our Mitsuri will be a gentle lady—she won't eat that much."
Yuri glanced fondly at the dazed toddler, unaware her daughter would become a fellow food monster.
Meanwhile, Yi Ren ignored the outside world, lost in his inner one.
Finally standing, he could test his swordsmanship!
Accessing the mental "book," he saw messy, ancient characters—even something resembling "Iron Mountain Lean" scrawled in blood-like strokes.
As he struggled, the text suddenly clarified, turning into moving figures that flowed into his mind.
Taking a deep breath, he grabbed a stick from the ground and clumsily swung it with his chubby arms—adorably awkward.
"Pfft! Yi Ren's hilarious—so cute!"
One nursemaid spotted him and melted, rushing over to smother him against her soft chest.
Yi Ren glared helplessly: Woman! Get off me! You're only slowing down my draw speed!
But at less than a year old, all that came out was baby babble—"eeh yaa yaa"—which only made him cuter.
"Waaah!! Let me hug him first!"
"Me next!"
The nursemaids swarmed, cooing and pinching.
Kaede-rin watched with a proud grin. "So charming already—takes after half of me, at least~"
"Kaede-rin-kun!"
Yuri's eyes sparkled with hearts, growing heated.
"What is it... Yuri?"
"Here—hold Mitsuri!"
She thrust the baby into his arms and dashed off with a declaration: "I'm going to squeeze him too!"
"..."
Kaede-rin twitched, staring enviously at the overwhelmed Yi Ren.
...
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