The late autumn evening breeze carried a hint of chilling malice, swirling the withered leaves in the courtyard.
Two days had passed since that Kasugai Crow broke the silence.
During these two days, the entire Demon Slayer Corps had entered an unprecedented state of maximum combat readiness.
All Hashira and swordsmen above Kinoe rank were secretly gathered at the Ubuyashiki Estate and its surrounding core hidden points.
The number of scouting eyeballs marked with the character "Four" in the periphery was increasing, like cold, omnipresent gazes staring fixedly at this area.
Everyone knew deep down that Muzan had locked onto their location.
That millennium-old Demon King could potentially emerge with all his Upper Ranks at any moment, or unleash some massive spatial technique to devour them all.
It was an oppressive atmosphere, like waiting for a death sentence.
Yet, there was one person who could still afford to be bored out of his mind at a time like this.
In the backyard of the Butterfly Mansion.
Yamada was wearing a wide black yukata, leaning lazily against a wooden pillar in the corridor.
In front of him was a small stove, with a few rice cakes grilling on top and a pot of sake warming beside it.
Tanjiro, Zenitsu, and Inosuke were currently sitting cross-legged in the center of the courtyard in an extremely bizarre posture. Their eyes were tightly shut, their breathing so faint it was almost inaudible, as they attempted to perceive the so-called "Transparent World" under Yamada's guidance.
"Don't knit your brows. Transparent World isn't achieved by forcing it. The more deliberately you try to think about it, the more distracting thoughts you'll have."
Yamada flipped the rice cakes on the stove and instructed casually, "Imagine your consciousness as a pool of stagnant water, where not even a pebble falling in can cause a ripple. Listen to the sound of the wind, the sound of the insects, and then listen to the sound of the blood flowing in your veins."
"How is that even possible to hear?"
Zenitsu was the first to break, frantically scratching his blond hair and rolling on the ground.
"My head is filled with that demon holding a fan. I'm going to die! I'll definitely be eaten in the decisive battle!"
"Useless coward, shut up! This great me has already heard it! I heard the rumbling in my stomach! It's the Boar God calling me!"
Inosuke jumped up abruptly, drew his dual blades, and started slashing wildly.
"That's because you're hungry." Yamada mercilessly punctured his fantasy.
He glanced at Tanjiro, who was still struggling to hold on.
He had the highest talent of the three, and his breathing frequency was already faintly tending towards nature.
"Alright, that's enough for today."
Yamada placed the grilled rice cakes onto a plate and poured a cup of sake. "Trying to cram at the last minute can only get you this far. Go clean your swords and get to sleep early tonight."
"Yes! Yamada-san!"
Tanjiro opened his eyes. Although he hadn't grasped Transparent World, his gaze was exceptionally firm.
Sending the three away, Yamada picked up his sake cup and took a sip.
Clack... Clack...
The sound of light geta sandals echoed in the corridor.
Shinobu walked over carrying a tray, on which sat several bottles of strangely colored concentrated potions.
She wasn't wearing her usual outfit today. Instead, she had changed early into the black uniform of the Demon Slayer Corps, with her butterfly-patterned Haori draped over it. Even her hair was tied up meticulously.
Clearly, she was also prepared for battle at any moment.
"Has the analysis of the Chakra samples been completed?" Yamada pointed to the medicine bottles in her hands.
"Yes."
Shinobu knelt down opposite Yamada and lined up the medicine bottles, a gleam flashing in her eyes.
"I mixed the Yang Release Chakra I extracted from you earlier with the highest concentration of Wisteria Toxin. Guess what? These two powers are a match made in heaven."
She picked up one of the light purple vials and shook it against the moonlight.
"Wisteria Toxin originally only destroyed demon cells in one direction. But your Yang Release can bestow life to forms. When these two are combined, I created a poison that can cause a demon's cells to 'overgrow' in an instant."
Hearing this, a trace of admiration flashed in Yamada's eyes. "Causing the cells to spiral out of control?"
"Exactly."
Shinobu's lips curved into a dangerous arc. "As long as this poison is injected into the bodies of Muzan or the Upper Ranks, their cells will proliferate wildly under the catalysis of the Yang Release. When the speed of division far exceeds the limits of their bodies... boom!"
She made an explosion gesture.
"Their regeneration will become a death warrant that accelerates their self-collapse. Furthermore, to prevent Muzan from decomposing the toxin, I also added the ingredients of the 'human transformation' drug sent by Tamayo-san."
Shinobu set down the medicine bottle, her eyes as cold as ice. "Aging, turning human, and cellular collapse. This is the triple hell I have prepared for Muzan."
Yamada listened to this description of what could only be called a terrifying biochemical weapon and couldn't help but raise an eyebrow.
Once this butterfly made up her mind, she was more lethal than the most venomous snake.
"Well done. Keep this medicine. When the decisive battle comes, find an opportunity to give him a heavy dose."
Yamada handed her a rice cake from the plate. "However, don't force yourself to engage in hand-to-hand combat with the Upper Ranks. With your strength, it's better to just hide behind me and shoot arrows."
Shinobu took the rice cake, bit off a small piece, and hummed with some dissatisfaction. "Stop looking down on me. Even if I'm not strong, I'm currently the fastest in the entire Corps."
"Yes, yes, the Insect Hashira is the best."
Yamada replied dismissively, but his gaze drifted over the courtyard wall towards the main house of the Ubuyashiki Estate.
The lights in the main house were still on.
Since recovering his health, Kagaya had barely closed his eyes these past few days. He was using the resources the Demon Slayer Corps had accumulated over a millennium to set the final trap.
Not only was he notifying swordsmen from all over to return for defense, he had even sent people to plant specially made gunpowder and Wisteria Toxin smoke bombs beneath the entire estate and in the surrounding woods, enough to level this mountain.