When Ren placed the Sound Hashira's head before Chitoshi's grave, it marked the beginning of his hunt against the Demon Slayer Corps.
Killing the Sound Hashira was not the end for Ren—it was merely the start.
Chitoshi would not die in vain. Ren vowed to offer the heads of every Corps member who spread rumors and accused him and his master to honor his brother's memory.
While Ren hunted the Corps, elsewhere, Yoriichi Tsugikuni, tracking Muzan Kibutsuji, encountered a former Corps comrade in a town.
"Lord Yoriichi!"
The young swordsman, once among Yoriichi's many admirers, still revered him despite Yoriichi's departure from the Corps, greeting him like a long-lost idol.
"I never expected to meet you here," Yoriichi said, surprised. He paid for a small snack, and they sat to talk.
"Anything happening with the Corps lately?" Yoriichi asked casually, popping a tricolor dango into his mouth.
The swordsman's face darkened.
"What's wrong?" Yoriichi pressed.
"Lord Yoriichi, do you really not know? Or are you pretending?"
Yoriichi frowned, clearly confused.
The swordsman gave a bitter smile. "Ren has become a demon."
"What?!"
Yoriichi froze, his first thought: Impossible.
"Don't lie to me!" His gaze turned icy, piercing the swordsman, his tone stern.
As Ren's master, no one knew his student better. He understood Ren's deep-seated hatred for demons and his near-obsessive resolve to slay Muzan.
To Yoriichi, even with his last breath, Ren would charge into battle against demons without hesitation.
How could someone who despised demons so fiercely fall to become one?
He couldn't accept it. In his eyes, Ren would never become a demon.
"It's true. It's no secret. Ask anyone in the Corps," the swordsman said, his face grim. "The Sound Hashira and Wind Hashira have already fallen to him."
"Have you seen Ren as a demon with your own eyes?" Yoriichi asked.
The swordsman shook his head quickly. "No, anyone who's seen him is dead."
"Then how do you know it was Ren?"
The swordsman shuddered, as if recalling something horrific, clutching his head. "Not long ago, Ren's Kasugai Crow flew over Corps headquarters. Then, the heads of those he killed rained down like a storm—among them, the Sound Hashira's two disciples and the Wind Hashira."
Boom!
The words struck Yoriichi like a thunderbolt, leaving him stunned, his body rigid, his mind blank.
He stared at the swordsman's face, searching for any hint of deceit in his pained expression.
But there was none. The truth was undeniable.
Could Ren truly have become a demon?
The thought crashed into his heart like a boulder, stirring a maelstrom of grief.
Master… The image of that youthful boy, his sunlit smile, flooded Yoriichi's mind.
Memories of their time together surfaced—Ren's fiery passion, his boundless energy.
How could that vibrant boy have fallen to become a despised demon?
His fists clenched, nails digging into his palms, oblivious to the pain.
No matter what, he couldn't accept it, couldn't believe that boy, radiant as summer's sun, had plunged into darkness, becoming a demon reviled by all.
Heaven, what did I do wrong?
His brother had become a demon, and now his beloved student followed the same path.
Was this punishment for failing to kill Muzan?
The faces of the Sound Hashira and Wind Hashira flashed in his mind. He recalled they were the loudest in demanding his seppuku when his brother, turned demon, killed the Corps' master.
Ren…
It had been years since their last parting. Yoriichi still remembered Ren's smiling wave goodbye.
Their letters over the years brimmed with Ren's hope for life.
What had happened to turn someone so hateful of demons into one?
Was it the Sound Hashira and Wind Hashira?
Did they target Ren?
Was it because of me?
Unable to find me, did they vent their hatred on Ren?
Yes, that must be it—the only explanation.
Even years after leaving the Corps, Yoriichi had heard the rumors.
They hadn't faded with his departure; they'd grown. But he hadn't cared. His life's sole purpose was to kill Muzan.
Whether in or out of the Corps, it changed nothing.
But if his absence caused Ren harm, he could never forgive himself.
Crack!
The glass cup in his hand splintered.
No matter the reason, he couldn't accept that his disciple, trained by his own hand, had become a man-eating demon.
Ren was his student, his swordsmanship born of Yoriichi's teachings. If Ren had truly become a demon and consumed humans, the responsibility fell first on him, the master.
Ren, have you truly fallen?
I will find you and learn the truth. If you've stepped into darkness, I must end you myself—then take my own life in atonement.