Taisho Era – Year 2 (1913)
Location: Azabu-juban, Tokyo
The winter air in Azabu was sharp enough to sting the lungs of any ordinary five-year-old, but Kai wasn't ordinary. He sat on a weathered stone step near the edge of a bustling merchant district, his small frame draped in a tattered, oversized kimono that had seen better decades.
Despite the grime of the streets, his appearance was striking. He possessed deep, burgundy-tinted hair tied back in a messy ponytail and eyes that held the clarity of a polished garnet. To any passerby, he was a ghost of a legend yet unborn—the spitting image of the Sengoku-era progenitor, Yoriichi Tsugikuni.
'Great Sage,' Kai thought, his gaze fixed on a stray cat stalking a frozen puddle. 'Status check.'
[Notice: Physical condition optimal. Ambient temperature is 2°C. Body heat regulation is functioning at 100% efficiency due to "Yoriichi-like Physique." Internal stamina reserves are vast for a child of five years.]
A small, satisfied smirk played on Kai's lips. It had been three months since he woke up in this world with nothing but a name and a set of memories that didn't belong to a beggar.
He knew the tragedy that awaited this world. He knew of the Twelve Kizuki, the tragedy of the Kamado family, and the bittersweet end of the Hashira.
But more importantly, he knew his neighbor.
Just a few houses down the hill, behind a gated wall that smelled of expensive incense and grilled eel, lived the Kanroji family. And among them was a girl with hair like cherry blossoms and eyes like spring grass: Mitsuri.
"Hey, little crow! You're staring at the wall again!"
The voice was boisterous. Kai blinked, looking up to see an elderly man carrying a basket of charcoal.
"I'm not staring, Old Man Sato," Kai replied, his voice surprisingly steady for his age, though he allowed a childish lilt to soften the edges. "I'm contemplating the structural integrity of the gate. It's a very fine gate."
Sato laughed, tossing a small, roasted sweet potato toward the boy. "You talk like a monk but look like a samurai. Eat up before you freeze."
Kai caught the potato mid-air with a reflex so fluid it looked like a blur. "Gratitude. You're quite the gentleman, Sato-san. If I were a girl, I'd be swooning."
The old man sputtered, his face turning red. "You cheeky brat! Where do you learn to talk like that?"
Kai just winked, his inner thoughts a whirlwind. 'Rule number one of surviving as an orphan: charm the locals. Rule number two: Great Sage, begin the calculation for Sun Breathing: First Form – Waltz.'
[Warning: Physical vessel is five years old. Attempting to execute "Waltz" will result in severe muscle fiber tearing. Recommendation: Continue "Total Concentration: Constant" foundations and basic physical conditioning.]
'Patience is a virtue,' Kai sighed. He peeled the potato, the steam rising into the cold air.
Later that afternoon, the gates of the Kanroji estate creaked open. Kai, who had positioned himself "coincidentally" on a nearby fence post, perked up.
A young girl, roughly his age, stepped out. She wore a high-quality kimono, her pink hair braided neatly. She looked like a doll, but there was an awkwardness in her movements—a hidden strength she didn't yet know how to control. This was Mitsuri Kanroji, years before the Demon Slayer Corps, years before the heartbreak of being rejected for her appetite.
She was currently struggling with a heavy wooden crate of supplies her mother had asked her to move to the side garden.
"Need a hand, My Lady?"
Mitsuri jumped, her eyes widening as she looked up at the fence. She saw a boy with strange, beautiful eyes smiling down at her. "Oh! Um, no, I'm okay! Mother says I'm very strong, but I shouldn't show off..."
Kai hopped down, landing silently on the snow. He walked over, his steps leaving barely a dent in the powder. "Being strong isn't a sin. It's a gift. Allow me."
He reached for the crate. Mitsuri blinked, "Wait, it's really heavy! I almost broke the—"
Kai lifted the crate. To him, it felt like a box of feathers. His "Yoriichi-like Physique" meant his muscle density was already transcending human limits, much like Mitsuri's own. He set it down exactly where she had been aiming.
Mitsuri stood frozen, her mouth slightly open. "You... you're very strong too."
Kai leaned against the crate, crossing his arms. He flashed her a grin—the kind that was far too confident for a five-year-old. "I have to be. How else could I protect someone as cute as you in the future?"
Mitsuri's face turned a shade of pink that rivaled her hair. She began to fidget with her sleeves, her heart racing. "Cute? You think... I'm cute?"
"I think you're a marvel, Mitsuri-chan," Kai said, his voice dropping into a softer, more sincere tone. He knew her insecurity—the fear of being "too much" for the world. "Don't ever hide your strength. Especially not from me."
[Notice: Emotional resonance detected. Target 'Mitsuri Kanroji' showing increased heart rate and positive hormonal response. Friendship/Affection bond initiated.]
'Good,' Kai thought. 'Step one: become the anchor she never had.'
"I'm Kai," he said, extending a hand. "I live... well, I live everywhere, but I'll be around here most days."
Mitsuri hesitated, then reached out, her small, powerful hand shaking his. "I'm Mitsuri. Are you... are you hungry, Kai-kun? We have leftover mochi!"
"I thought you'd never ask," Kai chuckled. "But before we eat, tell me—do you have any medical books in that big house of yours? Or maybe a kitchen I could observe? A man needs more than just strength to provide for a wife one day."
Mitsuri giggled, the sound like silver bells. "You're so funny, Kai-kun! You're just a little boy!"
"For now," Kai whispered to himself, his eyes shifting toward the darkening horizon where he knew the shadows of demons lurked. "For now."
As the sun began to set, painting the Tokyo sky in hues of violet and gold, Kai sat in the Kanroji garden, watching Mitsuri eat with gusto. While she was distracted, he closed his eyes, sinking into his mindscape.
'Great Sage, analyze the movements I saw from the swordsman in the market earlier today. Compare them to the theoretical data of the 'Breath of the Sun' from my memories.'
[Analysis in progress... Discrepancies found. Current world swordsmanship is degraded. Re-creation of 'Sun Breathing' requires 1,000 repetitions of basic swing forms to calibrate your unique physique. Would you like to begin the 'Medical Knowledge' archive download simultaneously?]
'Do it,' Kai commanded. 'I'm going to change everything. No one dies this time. Not Rengoku, not Shinobu... and definitely not the girl currently covered in bean paste.'
He looked at Mitsuri, who was happily telling him about a cat she saw. He smiled—a childish, friendly, and slightly mischievous smile.
The slow burn of his training was just beginning. In the heart of Azabu, a legend was being rebuilt, one mochi and one sword-swing at a time.