Seeing Kokushibo intervene in the battle, Rui immediately withdrew his threads and lowered himself from the battlefield.
Lower Rank Five understood instinctively: in the presence of Upper Rank One, even a single misstep meant death.
Kokushibo did not even look at him.
"Good judgment. That is why you survive."
He turned his attention to Tanjiro, calmly deflecting the boy's blade with minimal movement.
Tanjiro's strike was redirected effortlessly, the force dispersing into the air.
That scent
Tanjiro's eyes widened.
"It's you… you were at my house!"
Kokushibo paused for a moment, then answered without denial.
"Yes. I observed your home."
Tanjiro stiffened.
"You… observed my family?"
Kokushibo's tone remained calm, almost indifferent.
"It was not interference. It was observation."
Tanjiro's grip tightened.
Nezuko suddenly struggled within the web restraints, her body reacting violently as the threads tightened.
"Nezuko!"
Tanjiro rushed forward instinctively, but Rui responded immediately, reinforcing the threads.
Kokushibo lifted a hand slightly.
"Release her."
Rui obeyed without hesitation.
Absolute hierarchy.
Nezuko dropped to the ground, and Tanjiro immediately pulled her behind him, shielding her with his body.
"Why are you helping us?" Tanjiro asked, voice strained but respectful.
Kokushibo did not answer immediately.
Instead, he asked
"Tanjiro. Do you believe humans and demons can coexist?"
Tanjiro hesitated only briefly.
"No."
His voice sharpened.
"Demons are dangerous. They take lives. That cannot be forgiven."
Rui flinched slightly at the words.
Kokushibo, however, laughed softly.
Not mockingly at first almost contemplative.
Then louder.
A sound that unsettled even Rui.
"You speak of guilt so easily."
He stepped forward slightly.
"Tell me, Tanjiro are all demons guilty simply for existing?"
Tanjiro answered firmly.
"If they harm people… yes."
Kokushibo's expression remained unreadable.
"Then tell me this."
His voice lowered.
"Is it a sin for humans to consume animals?"
Tanjiro blinked.
"What…?"
Kokushibo continued without pause.
"Chicken. Fish. Livestock. All consumed to sustain human life."
Tanjiro frowned.
"That's different… humans need it to live…"
Kokushibo's eyes narrowed slightly.
"And demons need humans."
Silence fell.
The forest itself felt heavier.
"If survival is not sin," Kokushibo continued, "then why is only one form of survival judged?"
Tanjiro's words caught in his throat.
He tried to respond but nothing formed clearly.
Kokushibo watched him closely, as if dissecting his hesitation.
"Answer me, Kamado Tanjiro."
His tone sharpened.
"What is 'good'?"
Tanjiro forced himself to speak.
"Good is protecting people… helping others…"
"And evil?"
"Hurting others… taking lives…"
Kokushibo turned away slightly, as if disappointed in the simplicity of the answer.
"Convenient definitions."
He slowly sheathed his blade.
Then he began to circle Tanjiro.
Each step applied pressure without contact.
"Let me ask something simpler."
He stopped behind him.
"Must demons be killed?"
Tanjiro froze.
His mind immediately went to Nezuko.
To Tamayo. To the girl at the Butterfly Mansion.
His answer should have been simple.
But it wasn't.
Nezuko trembled slightly behind him, still weak but alive.
Kokushibo spoke again, softer now.
"Demons are born from humans."
A pause.
"Then humans created what they now condemn."
Tanjiro's eyes widened slightly.
Kokushibo stepped back.
"I will not kill you today."
He glanced at Rui.
"Nakime."
A moment later, space fractured beneath them.
The Infinity Castle began to open.
Wood and earth warped into impossible geometry.
Rui's body tilted as gravity itself shifted.
"Tanjiro," Kokushibo said calmly, "think carefully about what you believe."
Then both he and Rui vanished into the shifting architecture of the Infinity Castle.
Silence returned to Mount Natagumo.
Moments later, Demon Slayer Corps reinforcements arrived.
Shinobu Kocho surveyed the battlefield immediately, her expression tightening.
"Everyone, check injuries. Quickly."
Kyojuro Rengoku's voice rang out first from the distance.
"I am unharmed! Kamado boy, are you well?"
He stood upright despite injuries, still burning with energy.
Elsewhere, Sanemi Shinazugawa and Obanai Iguro bore serious wounds fractures and deep cuts sustained in battle.
Gyomei Himejima stood silently, hands clasped, having stabilized the situation after intense combat.
The Lower Rank threat had been eliminated.
But the Upper Rank presence was gone.
Shinobu narrowed her eyes slightly.
"Upper Rank One appeared… and left."
At the Butterfly Mansion afterward, the survivors regrouped.
The wounded Pillars were treated one by one.
Zenitsu and Inosuke were found separately Zenitsu injured and unconscious, Inosuke exhausted and bruised.
Most of Zenitsu's injuries were not from demons.
They were from Inosuke.
Despite everything, no casualties were recorded.
But the atmosphere was different.
Heavier.
Quieter.
Tanjiro sat alone under the night sky.
Nezuko rested nearby.
His hand tightened slightly on his broken blade.
"What is good… and what is evil?"
Far away, in the Infinity Castle, Muzan observed Kokushibo coldly.
"Why did you not kill him?"
Kokushibo stood beside him, composed as ever.
"Because killing him is not enough."
Muzan's eyes narrowed.
Kokushibo continued calmly.
"Breaking the body is easy."
A pause.
"Breaking belief lasts longer."