The moment the third possibility crystallized in his mind, Kaidō felt a chill run down his spine.
The very notion was absurd—every member of the Demon Slayer Corps harbored a blood-deep hatred for demons. How could they possibly slaughter an innocent family? Yet the more he examined the theory, the more the pieces began to fit together in ways that made his stomach turn.
If we eliminate the impossible, whatever remains—however improbable—must be the truth.
Setting aside Muzan Kibutsuji's ability to create demons, it was theoretically possible the Demon Slayer Corps had also developed that capability. Pure speculation, yes, but not beyond the realm of possibility.
Over a thousand years, the Hashira had slain countless members of the Twelve Kizuki. The Corps would have access to blood samples with high concentrations of Muzan's essence. They possessed combat abilities far beyond ordinary humans. They even kept demons imprisoned for research purposes.
But the most damning piece? Motive.
The emergence of a successor to Yoriichi Tsugikuni—the legendary first Breathing Style user—would pose a legitimate threat to Muzan's existence. The Demon King himself would fear such a warrior.
Kaidō wasn't suggesting every Corps member was complicit. His suspicions centered on one man: Kagaya Ubuyashiki, the Corps' master.
Kagaya had willingly sacrificed his wife and two of his children just to wound Muzan—a calculated move that spoke to ruthless pragmatism. Even Muzan had described Kagaya as "a cold, dangerous snake." High praise from a monster who'd lived for centuries.
There was no question that destroying Muzan was Kagaya's singular obsession. He would employ any means necessary to forge a swordsman capable of ending the Demon King's reign.
The strongest warriors in the Corps all share one trait: they harbor hatred for demons that burns hotter than hellfire itself.
To mold Tanjiro Kamado into such a weapon, Kagaya would first need to fill him with that same all-consuming rage. Which meant creating a tragedy so devastating it would reshape Tanjiro's entire existence.
So he killed them. Or had them killed.
As for why Nezuko was transformed into a demon—that was where the theory became truly disturbing.
The Ubuyashiki family had operated the Demon Slayer Corps for a millennium. Surely they'd conducted private research into Muzan's blood over the centuries. What if Nezuko had been selected as a test subject? That would explain why she alone among countless demons exhibited such unique characteristics.
Countless demons had retained fragments of their humanity, but not a single one had managed to resist consuming human flesh. None had achieved what Nezuko accomplished.
The appearance of Water Hashira Giyu Tomioka seemed to validate the hypothesis. Why would a Hashira just happen to be near the Kamado residence? Giyu had offered no explanation for his presence, but his focus on Nezuko had been unmistakable.
Giyu himself might have been oblivious to the larger machinations, but Kagaya could have orchestrated everything—a calculated gamble that modified Muzan's blood would prove effective.
Moreover, Giyu's timely arrival seemed explicitly designed to recruit Tanjiro into the Corps. But how had Giyu even known demons were at the Kamado household?
The Kasugai Crows.
Demons lurking in remote mountain regions rarely generated intelligence reports. Other demons Tanjiro had encountered in the wilderness went completely unnoticed by the Corps. Yet Giyu's crow had somehow delivered precise information about the Kamado residence.
The crows were trained exclusively by the Ubuyashiki family.
Another piece clicks into place.
Furthermore, the Ubuyashiki family had likely known for years that the Hinokami Kagura—the Dance of the Fire God—was preserved within the Kamado lineage. Just as Kagaya's wife, Amane Ubuyashiki, had located the descendants of Michikatsu Tsugikuni (now Upper Rank One, Kokushibo)—specifically, Muichiro Tokito, the current Mist Hashira.
While the Ubuyashiki family maintained historical records, those archives were neither comprehensive nor entirely intact. Despite this, they'd successfully traced bloodlines that had been lost for generations. If they could find completely disconnected descendants of the original swordsmen, locating the inheritors of the Fire God Dance would be trivial by comparison.
Another detail demanded attention: Why did Kagaya show such particular interest in these siblings? Why invest so heavily in Tanjiro's development while displaying no surprise whatsoever at Nezuko's condition?
The other Hashira's reactions spoke volumes—they'd been ready to execute both siblings on sight. Yet Kagaya had remained eerily calm, almost as if he'd expected everything.
A man capable of sacrificing his own family to kill Muzan would stop at nothing. It's a form of righteousness—and a form of cruelty.
Kaidō's thoughts twisted through the labyrinth of conspiracy, each connection leading to darker implications.
"But these are just theories. Speculation built on circumstantial evidence and paranoid pattern-recognition. What if I'm wrong? I'd be vilifying an innocent man who's devoted his life to protecting humanity."
Yet if he was right...
"Forget it." Kaidō exhaled slowly, forcing his racing thoughts to settle. "No use spiraling down rabbit holes I can't escape. When in Rome, as they say—or in this case, when in Taisho-era Japan. One step at a time."
His more immediate concern was practical: he'd overstayed his welcome.
"I need to leave soon. I've been here too long already. The Kamados have been incredibly generous—they'd never complain—but I can't keep imposing on their hospitality forever."
The thought triggered an unwelcome memory from his third day here. He'd been preparing to bathe when he'd entered the washroom and found Nezuko—completely naked—about to step into the tub.
God, that was mortifying...
They'd managed to clear up the misunderstanding, and Nezuko hadn't blamed him, but for several days afterward, both of them would flush crimson whenever they made eye contact. Kie Kamado had started giving them knowing looks, clearly suspecting some budding romance.
It had taken considerable effort to dispel that notion and restore normalcy between them.
'And why the hell am I thinking about that again? She's a child, for crying out loud. That's a one-way ticket to prison—three years minimum, death penalty maximum.'
Although, he had to admit, modern prisons weren't so bad. Three meals a day, running water, and if you were lucky, you might even find some soap in the shower—
"What the hell is wrong with me? These thoughts are getting progressively more disturbing." Kaidō scrubbed his face with both hands. "Focus. I need to prepare to leave, but I can't let Tanjiro and the others know I'm going."
"Kaidō-nii! Dinner's ready!" Hanako's cheerful voice called from outside.
"Coming, Hanako!" He rose to his feet and stepped outside, immediately ruffling the young girl's hair affectionately.
"Kaidō-nii, if you keep messing up my hair like that, I won't have any left!" Hanako protested, though her face was bright red.
"Don't worry, you'll be fine. Besides, you're going to grow up into an absolutely adorable young lady." He took her hand and started walking toward the house.
"Kaidō-nii, after dinner, can you tell us more stories? I love hearing your stories!" Hanako's eyes sparkled with anticipation.
"Sure thing. Whatever stories you want to hear tonight, I'll tell them."
"Yay!"
.....
The next morning, Kaidō rose well before dawn. He gathered his belongings—though "gathering" was generous, since his system's storage space held everything of value. He traveled light.
He placed a handwritten letter and fifty yen into an envelope. Fifty yen was pocket change to him, but for the Kamado family, it represented several months' worth of living expenses—enough to significantly improve their quality of life.
He deliberately avoided leaving more, knowing they'd refuse to accept it. They probably wouldn't even spend what he'd left, instead saving it to return to him when they next met.
Without disturbing anyone, Kaidō slipped out of the warm little house that had sheltered him.
...
"Kaidō-san, time to wake up! Breakfast is ready... Kaidō-san?" Tanjiro knocked on the door but received no response. He slid it open to find the room empty—only a letter resting on the table.
"Father, Mother—Kaidō-san left!" Tanjiro brought the envelope to where Kie was tending to Tanjuro.
When Tanjuro opened it, he discovered not just a letter, but fifty yen.
Tanjuro-san, Kie-san, Tanjiro, Nezuko, Hanako, Takeo, Shigeru, and Rokuta—thank you for everything during my stay.
Thank you for welcoming me as part of your family. But all good things must come to an end, and I have responsibilities I can no longer postpone.
Please accept this money—not as payment, but as a token of my sincere gratitude. If fate permits, I'll come visit again someday.
Tanjuro carefully refolded the letter and handed the money to Kie.
"That boy has a good heart. I hope he stays safe out there. I hope his future is bright." Kie's voice was soft with genuine concern.
"It will be," Tanjuro said with quiet certainty. "I can sense it—he's destined for extraordinary things. And I have a feeling Tanjiro will see him again sooner than we think."
From the moment Tanjuro had first met Kaidō, he'd known the young man was no ordinary person. The look in his eyes told a story—sorrow, regret, weariness, and beneath it all, a strange composure. He carried himself with a presence that didn't match his apparent age.
...
"Where the hell am I??"
After leaving the Kamado residence, Kaidō had wandered aimlessly for several days like a man without a map or compass. Now he found himself standing in a bustling town decorated with lanterns and festive banners, completely and utterly lost.
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~# Every 300 Power Stones = Bonus Chapter!
~# Add to Library!