Spring faded, autumn arrived, and a year slipped by swiftly.
Horitake thrived on Peach Mountain. Though Jigoro Kuwajima, his quirky master, could be eccentric, his knowledge was vast. Horitake absorbed countless skills from the old man, who was delighted with his diligent, gifted apprentice. Jigoro taught generously, holding nothing back.
The first six months, Horitake honed his physique and swordsmanship. The next, he began mastering Thunder Breathing while continuing to build his strength. Thunder Breathing, one of the five primal techniques, was fierce and relentless, its swordplay swift and unstoppable. Its power was extraordinary.
After rigorous training, Horitake felt it: Thunder Breathing was taking root. On a winter day, it clicked naturally, like water finding its course. In the snowy clearing, he crouched, feet planted, center low, left hand on his scabbard, right gripping the hilt.
He inhaled, air flowing in a mystic rhythm. "Thunder Breathing, First Form: Thunderclap and Flash!"
In an instant, electric arcs crackled around him. His blade flashed free, and he surged forward like lightning. A glint of steel, then the sword returned to its sheath.
Crack! Boom! Behind him, a peach tree as thick as a bucket split and crashed into the snow, stirring a flurry. Horitake grinned, satisfied. Thunder Breathing was his—a year's toil rewarded.
A chill of menace pricked his senses. Jigoro appeared behind him, eyes glinting like a demon's, dark aura swirling. "You little punk! Another peach tree ruined! Sine!" he growled.
Horitake bolted. "Sorry! Sorry! Azuki-mud gomenasai!"
In the snow, master chased apprentice, weaving through countless peach trees until they stopped, breathless. Horitake, panting, raised a fist in mock protest. "Old man! It's just one tree! This mountain's drowning in them!"
Jigoro fumed. "You've been here a year and wrecked who-knows-how-many trees!"
"What else am I supposed to practice on?" Horitake shot back. "Peach Mountain's got nothing but peach trees! And you didn't even notice—I mastered Thunder Breathing's First Form! No praise, just grief over trees. Are they your apprentice, or am I?"
Jigoro paused, sheepish, then feigned gravitas. "Well, First Form, huh? Slower than I was, but not bad."
"Are you praising me or insulting me, old man?!"
"Praise, you brat! Obviously!"
"Sounds like an insult to me!"
Their daily bickering flared up again. Over time, Horitake and Jigoro had grown close. Jigoro, a gruff old child at heart, adored his apprentice despite his stern facade. Horitake, cheeky and irreverent, respected his master deeply beneath the banter. Their squabbles brought warmth to the quiet mountain.
After the commotion, Jigoro coughed, regaining composure. "Not bad, kid. You've entered Thunder Breathing. Keep training—don't slack. Oh, and chop that tree into firewood. It's an eyesore."
"Got it, naggy old man," Horitake muttered.
Alone in the snow, Horitake gazed at the gray sky, melancholy stirring. It was Taisho Year Two, the year Tanjiro's family would be slaughtered, marking the tragic start of Demon Slayer. In his year on the mountain, Horitake had searched nearby towns for the Kamado family, but found nothing. Japan was vast, and tracking them was like seeking a needle in the sea. He couldn't stop their tragedy.
The snow, the year—it might be happening now. Shaking off the thought, Horitake focused on the present and future. He couldn't change the past, but he'd prevent future tragedies. That was his life's mission.
Reigniting his resolve, he practiced Thunder Breathing's First Form again, its ferocity flowing smoother each time. In the original story, Kaigaku never mastered this move. Horitake had—proof he was breaking fate.
Then, a chime rang in his mind: "Ding! Host has broken fate, triggering a butterfly effect. System activated!"
Horitake froze, sword still, stunned in the snow. A system? My cheat code's finally here? After years in this world, it was late—but not too late. The story was just beginning.
Half-exasperated, half-thrilled, he muttered to the system, "Alright, what's your deal? What can you do?"
The system's voice was flat, almost robotic. "Ding! This is the Butterfly Effect Control System, designed to manage negative butterfly effects caused by the host and aid in becoming stronger."
Horitake frowned. "I get butterfly effects, but controlling them?"
"Ding! Uncontrolled effects accumulate, leading to catastrophic outcomes."
"Fine, you're the system, you're right. You said 'negative' butterfly effects? They come in positive and negative?"
"Correct. For example, as a child, you avoided being taken in by Gyomei Himejima, preventing his imprisonment—a positive effect, so the system remained dormant. Now, mastering Thunder Breathing's First Form has triggered a negative butterfly effect, activating the system."