The instant the door swung open, all nine Hashira saw Muzan's grotesque state.
At the same time, behind him, they glimpsed the fierce battle raging deep within the Infinity Castle.
A bolt of lightning interwoven with black and gold was tearing through the castle, streaking back and forth. Wherever it passed, demons withered and fell—almost none could withstand it.
In that fleeting overlap of moments, the Nine Hashira met Kurosaki Rei's gaze across the distance. Their eyes were filled with trust.
Sweat beaded faintly on Muzan's brow. His situation now was a wolf in front and a tiger behind. After weighing it all, he decided Nezuko was still the more "palatable" target—trying to eat Kurosaki Rei would take far too much effort.
So he "gathered his courage" and stepped through the door, charging straight at the Nine Hashira.
He was the Demon King, after all—possessing endless lifespan and regenerative power far beyond that of the Twelve Kizuki. With ten hours still left until dawn, he believed he could simply grind these Hashira down by attrition!
"Muzan!"
Amid an angry shout, a streak of golden lightning flashed past, causing Muzan to instinctively dodge, veering far to the side.
Only after avoiding the strike did Muzan feel a surge of irritation—because he realized the attacker was merely a kid, not particularly strong. And yet, he had instinctively dodged in fear.
For a split second, he had thought Kurosaki Rei was coming for him again. Instead, it was just a brat using Thunder Breathing.
"Boar Rush! Boar Rush!"
From the flank came an energetic shout. Muzan had barely begun to turn when the Stone Hashira's attack was already upon him, forcing him to deal with Gyomei first.
This time, prepared, he reinforced his body with Blood Demon Art and met the blow head-on.
Boom—!
To Muzan's shock, even after assuming such a grotesque defensive form and bracing himself, he was still sent flying by Gyomei's strike. The震荡 force nearly shattered his internal organs.
Fortunately, his regenerative ability was extraordinary, healing the damage in an instant—but Gyomei's threat level skyrocketed in his mind.
Staring at the earth-yellow markings on the Stone Hashira's face, then recalling the dark purple-black patterns on Kurosaki Rei earlier, Muzan's expression turned grim.
He had seen Demon Slayer Marks before. He was certain—this wasn't one of them. Especially since Gyomei was clearly not young, yet the markings carried no obvious burden.
Had the Demon Slayer Corps evolved again? Mastered a technique even more advanced than the Mark?!
The weight in Muzan's heart deepened. At the same time, he felt grateful for his "decisiveness" tonight. Coming to the Demon Slayer Corps had been the right call—he had to become immune to sunlight as soon as possible, or facing the Corps would only grow harder in the future.
He had already decided: once he seized Nezuko, he would retreat immediately. As soon as he became a sun-immune demon, he would leave this country at once and find a new place to start a new life.
As for partners like Kokushibo?
Let him die.
Once Muzan perfected himself, all subordinates would be unnecessary. A perfect, immortal being needed only one king—there was no reason to share the throne.
The Nine Hashira and Muzan clashed fiercely. Tanjiro couldn't help but climb onto the wall to watch. If not for the Hashira's insistence that someone must stay by Nezuko's side to guard against a surprise attack from Muzan's underlings, he would have already rushed out to fight Muzan himself.
Lady Tamayo also emerged from the house, watching the battle outside the courtyard with a grave expression, hatred burning in her eyes.
"Why… has my regeneration slowed?"
After fighting for some time, Muzan realized he couldn't quickly deal with the Nine Hashira. Worse still, he sensed that his regeneration was no longer as rapid as it had been at the start.
Then he noticed Tamayo's gaze from atop the wall and roared in fury, "Tamayo—what did you do to me?!"
Aside from slowed regeneration, Muzan felt another force inside him, constantly draining him, eroding his demon cells from within.
"Oh?" Tamayo's lips curved upward. Seeing Muzan's wretched state filled her with satisfaction.
"Shouldn't you be asking the Hashira what they did to you instead?"
The results of the two months of research she and Shinobu had conducted were finally taking effect. Following Kurosaki Rei's suggestion, the drugs targeting Muzan weren't limited to what Shinobu stored in her syringe-like Nichirin blade—every Hashira had coated their blades with highly concentrated toxins.
Even the most upright Flame Hashira had raised no objection. Against an abomination like Muzan, who needed martial honor?
Thus, all the Hashira were using poison—and mixed toxins at that.
They included a drug capable of turning demons back into humans, as well as another that drastically accelerated Muzan's lifespan depletion.
The so-called immortal Demon King was only immortal in relative terms. Tamayo estimated that even demons, with ample nourishment, could live at most around ten thousand years. Muzan, as the progenitor, might reach twenty thousand at best.
Her toxin caused Muzan to age fifty years every minute.
On top of that was Shinobu's wisteria-based poison, which inflicted continuous damage on demon cells.
So now, facing nine Hashira at their peak, all with Ghost-God activated, Muzan was being smashed head-on. The longer the fight dragged on, the more wrong it felt—an unmistakable sense of exhaustion crept in.
While the Nine Hashira battled Muzan outside, the Infinity Castle presented an entirely different scene.
"Hahaha! Exhilarating! This is the first time I've ever met a man as strong as you! Come—keep fighting!"
Akaza, missing arms and legs moments ago, charged at Kurosaki Rei again the instant he regenerated, laughing wildly as he hurled a punch at Kurosaki Rei's head.
By now, he no longer cared about being outnumbered. Kurosaki Rei's strength had proven that even under siege, he could effortlessly slaughter the other demons in the Infinity Castle—and had casually shattered Akaza himself multiple times.
"How pitiful."
After forcing Kokushibo's blade back with a slash, Kurosaki Rei spun and swept a kick behind him. Reinforced with Armament Haki, the kick directly blew Akaza apart.
Kurosaki Rei drew a deep breath. The power of Thunder Breathing made his offense fierce and domineering. Regaining his footing, he brought his blade down again at Kokushibo.
With the title bonus assisting his strength check, he knocked Kokushibo flying, then immediately turned and charged at the regenerating Akaza.
Akaza truly loved combat and pursued strength his entire life—but he had forgotten why he became a demon in the first place.
His life had been tragic. The fists he honed to protect others were never put to use. His respected master and fiancée were poisoned to death by a rival dojo's underhanded schemes. He later slaughtered those responsible with his bare hands, but it did nothing to bring back his loved ones.
Kurosaki Rei empathized deeply with Akaza's fate—had his own life been any different?
Once, he too had a beloved master and senior sister, only to lose them to villains. He completed his revenge, yet became a wandering ghost with no purpose left in life.
Thus, in his heart, Kurosaki Rei was grateful to the Terminal Space. It had given him a second life—and with it, a reason to live again.
He would overcome all forms of the supernatural and reach the pinnacle of martial arts.
He would make his name resound across all worlds, so that his master and senior sister in heaven could hear it and know he had not failed their teachings.
And perhaps, through the miracles of the Space, some tragedies could even be reversed.
Akaza was not so fortunate.
After his master and wife died, he lost all meaning in life, drifted aimlessly, and encountered Muzan. Turned into a demon, his memories were sealed by Muzan to better exploit his strength—leaving behind only a battle-crazed man obsessed with becoming stronger.
In truth, Akaza had long wished for death. He only wanted to reunite with his master and wife—but Muzan kept him wandering the world as a demon for hundreds of years.
"I'll send you on your way."
Kurosaki Rei reached Akaza and swung his Zanpakutō in a horizontal arc. Violet-gold blade light flashed, severing Akaza's head.
In the instant his head separated from his body, Akaza's eyes first grew confused, then sorrowful. When he looked at Kurosaki Rei one last time, gratitude flickered within them.
"May you reunite with those you long for…"
Kurosaki Rei said softly, then turned and blocked Kokushibo's incoming blade with a single slash.
"What a rude fellow…"
Sliding back as he dissipated the force, Kurosaki Rei frowned.
"I really hate it when someone interrupts while I'm talking."
It had already been more than ten minutes since the battle began. Facing Kokushibo and Akaza together, Kurosaki Rei had been darting through the three-dimensional battlefield of the Infinity Castle, slaughtering vast numbers of demons along the way.
Now, aside from him and Kokushibo, there were likely fewer than ten demons left alive.
"So it's just the two of us now. Good. That way, you won't be running away anymore."
Kokushibo did not pursue. He held his blade across his side.
"Come. Now it's time—for a battle between just the two of us."
Kurosaki Rei pulled out a black pill from his storage and swallowed it. It was a soul-source recovery item he had purchased earlier. Maintaining Ghost-God at high intensity for so long, and using high-level Kidō, had heavily drained his soul power.
Just as he swallowed the pill, Kokushibo's words nearly made him choke.
After forcing it down, Kurosaki Rei tilted his head, looking at Kokushibo in confusion.
"When did you get the idea that I was running away?"
From the start of the fight until now, he had indeed been relying on Thunder Breathing and Shunpo-level mobility to move throughout the Infinity Castle—but that was to hunt demons, to chase Qingfeng and Dōma. Since when did that count as fleeing?
"Isn't it?" Kokushibo shifted to a two-handed grip.
"Then let me see your true strength—face me head-on."
From Kokushibo's perspective, Kurosaki Rei had never engaged him in prolonged exchanges. Every time, after blocking a move, Kurosaki Rei would disengage to slaughter other demons. To him, that looked like avoiding a direct duel.
He admitted Kurosaki Rei's speed was incredible—far beyond his own—but that was movement speed. In close combat, whose blade was faster was another matter entirely.
He believed that in a frontal clash, he would not lose. He had absolute confidence in the Moon Breathing he had refined over centuries.
Compared to the past, he was stronger now. Even if his younger brother were to return, he believed the victor would be himself!
"You're Tsugikuni Yoriichi's older brother, aren't you?"
Kurosaki Rei spoke while feeling the recovery item take effect. His soul power was steadily rising, having crossed the 50% mark.
"Don't you dare mention that name!"
Like a cat whose tail had been stepped on, Kokushibo erupted in fury, glaring at Kurosaki Rei.
"Oh? That hit a nerve?" Kurosaki Rei chuckled.
"Don't tell me you still lost after becoming a demon? Or maybe—you got one-shot by your elderly, dying brother?"
Kurosaki Rei smiled. He had no habit of taunting enemies in battle—but seeing Kokushibo's expression was simply too entertaining.
As expected, Kokushibo's face darkened like charcoal. His voice sank low.
"What… exactly are you?"
At this point, Kokushibo was convinced Kurosaki Rei wasn't human—no, he believed Kurosaki Rei was an "original demon" like Muzan.
Otherwise, how could Kurosaki Rei know so much of the past? How could he use Blood Demon Art?
"Me?"
Kurosaki Rei adjusted his breathing. As he spoke, the lightning around him surged even more violently.
"Of course I'm human."
The moment the words fell, Shunpo activated.
Amid crackling electricity and explosive air pressure, Kurosaki Rei surged forward like a raging thunderbolt, instantly appearing before Kokushibo—Demon-Imprisoning Blade slashing straight for his neck.
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