Horitake grappled with the system's explanation. "I get it—my better character spared Gyomei from prison, a positive butterfly effect. But mastering Thunder Breathing's First Form is good too! Why's it negative?"
The system's flat voice echoed in his mind: "Butterfly effects involve unpredictable causality. Positive and negative outcomes each have a fifty percent chance."
"Fine. What's this negative effect I caused?"
"Ding! By mastering Thunder Breathing's First Form, you've triggered a negative butterfly effect: the protagonists, Tanjiro Kamado and Nezuko Kamado, face imminent death!"
"What?!" Horitake leapt up, heart racing. "My future wife and brother-in-law are gonna die because I learned First Form?! I wouldn't have if I'd known! What do I do?!"
Wailing in the snow, he forced himself to calm down, thinking frantically. "I wasn't thorough watching the anime—I don't know where the Kamados live. I couldn't find them! How do I save them? My wife! My brother-in-law!"
A spark hit. "Kisatsume Mountain! They're heading there! I'll track that direction. The old man must know where it is! And Tomioka Giyu—he's met them by now. He could help! But… is there time? System, what does 'imminent' mean? How long do I have?"
The system's tone seemed almost exasperated. "Ding! Calm down, host. My purpose includes helping you resolve negative butterfly effects."
"Then hurry up!"
"Ding! Task issued: Prevent the negative butterfly effect—save Tanjiro and Nezuko Kamado from death. My navigation function will guide you to them. Your current strength, with caution, is sufficient to face their threat. Note: 24 hours remain until their death. Act swiftly.
Reward: Advanced Thunder Breathing First Form: Thunderclap and Flash.
Penalty: Tanjiro and Nezuko die, you lose your future wife and brother-in-law, fate shifts drastically, and butterfly effects collapse further."
Horitake stared, piecing it together. Positive effects were ignored; negative ones triggered tasks he'd solve, with rewards to grow stronger. Brilliant!
A 24-hour countdown appeared in his vision's corner. "Nice work, system! I'm off!"
He sprinted home, bursting into Jigoro's house, nearly toppling the door. Grabbing supplies, he shouted, "Old man, I'm taking this coat—it's warm! Your spare Nichirin Blade too! And these rice balls for the road!"
Jigoro's forehead pulsed with veins. "What are you doing, brat?!"
Horitake, already packed, bolted down the mountain. Jigoro yelled from the doorway, "What's going on? Where are you going? When are you back?"
From the trees, Horitake's voice echoed, "Finding my future wife and brother-in-law! Don't worry, back in a few days!"
Jigoro, stunned, blinked. "Wife? Brother-in-law? I didn't know about this! Was this why he kept leaving?" Petals swirled as he daydreamed, "Good for him, thinking of marriage. Wonder what the girl's like—pretty? Kind? Worthy of my brat?"
Meanwhile, Horitake raced along the system's guided path, heart pounding. I'll make it. The system wouldn't give me an impossible task. Using Thunder Breathing's rhythm, he stretched his stamina and speed, possibly nearing Total Concentration Breathing. Nezuko, my future wife, you'll be fine! Tanjiro, you too—can't let the plot derail, or my foresight's useless!
He ran for 24 hours, eating rice balls when hungry, sipping stream water when thirsty, resting briefly when exhausted. Sleep? No time.
As the countdown neared its end, what danger loomed for the Kamados? Normally, their journey to Kisatsume Mountain faced only a temple demon at the end. But this negative butterfly effect brought a new threat—a demon with unique powers.
"Nezuko!" Tanjiro's desperate cry rang out.
The protective brother was now protected. A demon ambushed them on their path, too strong for Tanjiro. Nezuko, now a demon herself, fought fiercely to shield him. Clutching his bleeding arm, axe in hand, Tanjiro watched helplessly as Nezuko battled the demon evenly.
The demon wasn't overwhelmingly strong, but its special ability had injured Tanjiro. Staring it down, he saw its mouth open and shouted, "Watch out!"
The demon spat four fangs like darts. Nezuko dodged, but one struck her back.