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Night fell over Mount Sagiri. After finishing dinner with Urokodaki, Kaidō retreated to his room and closed the door behind him.
"Alright, time to collect my rewards." He'd completed the Final Selection days ago, but he'd deliberately held off on claiming the quest completion. Too many distractions, not enough privacy.
[Ding! Quest Complete: Journey to Mount Sagiri, seek training from Sakonji Urokodaki, and participate in the Final Selection.]
[Rewards: Phantom Eye, Mental Enhancement Serum x2, Dragon Breathing Seventh Form, Dragon Breathing Eighth Form, 100,000 Yen.]
[Ding! Congratulations! Host has completed their first major quest. Bonus reward: 8% Interdimensional Energy.]
[Current Interdimensional Energy: 15%]
Kaidō's heart slammed against his ribs. "Holy shit—that's huge! I'm already at fifteen percent total. At this rate, I'll be home before I know it!"
The thought of seeing his mother again, his sister, even that idiot Hayato—it made his chest tighten in ways he hadn't felt since the transmigration.
He forced himself to breathe. Focus. There's work to do first.
"Okay, let's think this through. I've got nine Dragon Breathing forms now—I developed the Ninth Form on my own while waiting for the quest to complete so I could unlock the Seventh and Eighth. Now that I've got all nine, I need to master them before my sword arrives."
He paused, staring at the system interface.
"The system gives incredible rewards, but they're useless if I can't properly integrate them into my fighting style. Power without skill is just wasted potential."
Decision made, he selected the Phantom Eye reward.
[Ding! Fuse Phantom Eye? Warning: The fusion process will cause severe ocular pain. Please prepare yourself.]
Kaidō took a deep breath, then another. "No guts, no glory. Do it."
[Beginning fusion... Fusion in progress...]
"FUCK—"
The pain hit like a railroad spike driven directly into his left eye socket. It wasn't just pain—it was violation, like someone had taken a red-hot knife and was carving patterns into his eyeball from the inside out, twisting, scraping, reshaping.
His hands clenched into fists so tight his nails drew blood from his palms. Sweat poured down his face. He bit down on his sleeve to keep from screaming and waking Urokodaki.
Thirty goddamn minutes of agony that felt like thirty hours.
[Ding! Fusion successful.]
Kaidō collapsed onto the tatami mat, gasping. "Finally... that was worse than dying the first time around."
His left eye felt different—not painful anymore, but strange. Foreign. Like it belonged to someone else and his brain was still learning how to use it.
"I'll test it tomorrow. Right now, I need the mental boost if I'm going to function." He pulled out both vials of Mental Enhancement Serum and downed them one after the other without hesitation.
Immediately, his head felt like it weighed a thousand pounds. The room spun. His vision blurred. For a few terrifying seconds, he thought he'd made a massive mistake—
Then clarity.
His thoughts sharpened like a blade fresh from the whetstone. The fog that always seemed to linger at the edges of his consciousness vanished completely, replaced by crystalline focus. Mental calculations that used to take effort now came effortlessly.
"Damn. This is going to be useful." Kaidō grinned despite the exhaustion. "Tomorrow, I'll test everything properly. Once I've mastered these new abilities, I'll be ready for whatever bullshit this world throws at me."
...
The next morning, Kaidō climbed to the mountain peak hoping to find Sabito and Makomo. He wanted to tell them he'd officially become a Demon Slayer, that their deaths hadn't been in vain.
But the summit was empty.
"Maybe that's for the best," he murmured, kneeling before their graves. "We'll meet again when the time's right."
Sabito's voice drifted on the wind, though Kaidō couldn't hear it. "Should we go see him?"
Makomo shook her head gently. "He understands. He knows we're watching."
...
Kaidō made his way to the river to wash his face. The moment he looked at his reflection in the water, he froze.
His left eye—formerly golden like the right—now gleamed with a vivid purple hue, the color of amethyst catching sunlight.
"Well, that's new." He leaned closer, studying the change. "This must be the Phantom Eye. Guess heterochromia is my life now."
Time to test it.
Kaidō closed both eyes, centering his breathing. Then he opened them—focusing specifically on activating the Phantom Eye.
The world... slowed.
Not stopped, but stretched like taffy pulled between two hands. A butterfly drifted past his face, its wings beating in slow motion, each individual scale visible. The river flowed like honey instead of water. Every falling leaf, every swaying branch—he could perceive it all with perfect clarity.
"This is insane..." His grin widened. "If I use this in combat, I'll be able to read enemy attacks before they even finish the motion. I'll see openings that don't exist for normal people."
But that was only half the ability. The Phantom Eye also created illusions—trapped enemies in false realities constructed from their own desires and fears.
Kaidō glanced up at a small bird perched on a nearby branch. "Sorry, little guy. Science requires sacrifice."
He focused his left eye on the creature. "Illusion."
The bird immediately toppled from its perch, landing in the grass with a soft thump.
Kaidō could see the illusion he'd trapped it in: dozens of other birds surrounding it, bowing in reverence like subjects before a king.
"Even birds dream of greatness, huh?" Kaidō chuckled—then immediately regretted it as vertigo slammed into him like a freight train.
His head felt like someone had filled it with lead. The world tilted sideways. He staggered, nearly falling into the river before catching himself.
"Okay, note to self—illusions burn through mental energy like crazy. Can't spam that in combat or I'll pass out at the worst possible moment." He took several deep breaths, waiting for the dizziness to fade. "But used strategically? One second of hesitation from an enemy is all I need to turn a fight around. This could be a genuine lifesaver."
The bird woke up a moment later, shook itself off, and flew away—probably very confused but otherwise fine.
Kaidō splashed cold water on his face and got to work.
...
Fifteen days passed in a blur of relentless training.
Every morning, Kaidō pushed his Total Concentration Breathing to its absolute limits—no more interruptions, no more breaks in rhythm. He'd learned from the Final Selection; those traps that disrupted his breathing had taught him a valuable lesson about maintaining focus under pressure.
His Dragon Breathing forms became second nature. What had once required conscious thought now flowed as naturally as breathing itself—which, considering that's literally what they were based on, made sense.
He practiced with the Phantom Eye daily, gradually extending the duration of his illusions. Thirty seconds. That's how long he could maintain a mental construct now before exhaustion set in.
Thirty seconds didn't sound like much, but in a life-or-death fight, it was an eternity.
"Today's the day," Kaidō said aloud, stretching his arms overhead. "Fifteen days are up. My sword should arrive any minute now."
As if summoned by the words themselves, a figure appeared on the path leading to the house—a swordsmith wearing a distinctive hat adorned with dozens of wind chimes and a Hyottoko mask covering his face.
"I am Hotaru Haganezuka," the man announced, his voice sharp with barely contained irritation. "I'm here to deliver a Nichirin Blade to Ryūjin Kaidō. Where is he? I have questions."
"That'd be me." Kaidō stepped forward. "Something wrong?"
"WRONG??" Haganezuka's voice rose to a near-shriek. "You requested the most absurdly impractical weapon I've ever been asked to forge! It consumed three times the normal amount of scarlet ore and scarlet crimson iron sand! It's ridiculously heavy! Unnecessarily large! And—"
"It's perfect for my Breathing Style," Kaidō interrupted calmly. "Dragon Breathing requires reach and weight to maximize impact. A standard katana wouldn't work—I need something with real mass behind it. Besides, the extra training weight will only make me stronger."
Haganezuka went silent for a moment, processing this.
"I see. So this... greatsword... as you called it in your design—it's not just aesthetic preference. It's functional necessity." The swordsmith's tone shifted slightly, moving from outrage toward grudging respect. "And you're confident you can wield it effectively?"
"Completely."
"Hmph. Very well." Haganezuka pulled a long wooden case from his back. "Nichirin Blades are also called 'color-changing swords'—they reflect the wielder's nature. Let's see what color your greatsword becomes. I'm hoping for Bright Red—the legendary blade of the sun."
They moved inside. Urokodaki watched with quiet interest as Kaidō opened the case.
The weapon inside was magnificent.
A meter-long blade, thirty-centimeter grip, twenty centimeters wide at its broadest point. It was massive—designed to cleave through demons rather than simply cut them.
Kaidō lifted it from the case, feeling the weight settle into his hands. Heavy, yes, but perfectly balanced. He drew the blade from its sheath, gripping the handle with both hands.
The metal began to change.
From base to tip, the entire blade shifted—flowing like liquid color until it settled into a deep, vivid crimson. Not quite red, but close. The color of fresh arterial blood.
"BRIGHT RED! IT'S BRIGHT RED! THE LEGENDARY—" Haganezuka practically vibrated with excitement. "I finally forged a Bright Red blade! After all these years! HAHAHAHA!"
"Haganezuka-san, calm down!" Kaidō tried to interject. "It's not actually bright red—look closer!"
Urokodaki stepped forward, examining the blade with a critical eye. "He's right. It's blood-crimson, not true bright red. Close, but not quite the legendary sun blade."
Haganezuka deflated slightly. "Ah... you're correct. How disappointing." He jabbed a finger at Kaidō's chest. "But mark my words, Ryūjin Kaidō—you will treat this weapon with respect! If you break it or lose it, I will hunt you down and make you regret it!"
Kaidō immediately thought of Tanjiro getting chased through the streets by a knife-wielding Haganezuka and suppressed a laugh. "Understood. I'll guard it with my life."
At that moment, Kuroha swooped through the window and landed on Kaidō's shoulder, ruffling its feathers importantly.
"CAW! Kaidō! Master summons! Proceed immediately to Demon Slayer Corps Headquarters! Master summons! Proceed immediately!"
"Hey, Kuroha! Long time no see, buddy!" Kaidō immediately scooped up the crow, scratching under its chin. The bird cooed contentedly, nuzzling against his hand.
He turned to Urokodaki. "Looks like it's time, Master. Thank you for everything you've taught me. And..." He touched the fox mask hanging from his belt. "Thank you for this. I'll treasure it."
"You've learned everything I can teach you," Urokodaki said quietly. "The path ahead is yours to walk. But when you reach Headquarters, do me a favor—check in on Giyu Tomioka. He's your senpai. Make sure he's doing alright."
"I will." Kaidō strapped the greatsword across his back, the weight already feeling natural. He positioned the fox mask at an angle on his head—not covering his face yet, but ready to drop into place when needed.
"And Haganezuka-san—don't worry. I'll put your craftsmanship to good use. Every demon I kill with this blade is a testament to your skill."
"Hmph. Make sure of it."
Kaidō walked to the door, pausing at the threshold to look back one final time. He raised his hand in farewell. "See you later, Master!"
Then he stepped outside, following Kuroha as the crow took flight toward Corps Headquarters—and his meeting with the enigmatic Kagaya Ubuyashiki.
Urokodaki watched him go until he disappeared from view, then whispered to the wind:
"May fortune favor you in battle, my student. Come back alive."
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~# Every 300 Power Stones = Bonus Chapter!
~# Add to Library!