Chapter 199: Infinity Castle (Part 1)

"Thunder Breathing, Second Form: Rice Spirit." The young Demon Slayer swiftly approached the motionless Upper Rank demon from behind, delivering a five-strike combo enhanced by his Breathing Technique to the demon's neck.

The Upper Rank demon didn't react, allowing the boy's attacks to land on his neck. Each strike produced bright sparks, but unfortunately, the demon's neck remained unscathed.

"Thunder Breathing, Third Form: Thunder Swarm."

"Thunder Breathing, Fourth Form: Distant Thunder."

"Thunder Breathing, Fifth Form: Heat Lightning."

"Thunder Breathing, Sixth Form: Rumble and Flash."

The young Demon Slayer unleashed all his learned forms of Thunder Breathing, but none of them inflicted any damage on the Upper Rank demon before him. Fear filled the boy's eyes as he turned and fled, abandoning the fight.

The Upper Rank demon looked slightly puzzled as he watched the boy run away. Without making a visible move, he suddenly appeared behind the fleeing boy, slashing his right arm off with his sword.

Thud.

The dismembered Demon Slayer fell to the ground, tumbling several times before sliding to a stop. 

"Don't kill me! I don't want to die! I'll do anything if you spare me," the boy pleaded, crawling up and kowtowing before the Upper Rank demon, disregarding his injury.

The Upper Rank demon hesitated, lowering his sword. After a moment, he retracted his weapon.

"You don't want to die? Then become a demon." The demon approached the boy, using his left hand to cut his own palm, producing a large drop of demon blood.

He held out his hand, offering the blood to the boy. Without hesitation, the boy licked the demon's palm, drinking the blood. Immediately, he screamed in agony.

"Whether you survive or not depends on if you can assimilate this blood. If you can't, you'll die," the Upper Rank demon stated coldly.

Becoming a demon wasn't easy. Just as not all Demon Slayers could master Breathing Techniques, not everyone who received blood from an Upper Rank demon or Muzan could become a demon. It depended on their ability to assimilate the blood.

When Muzan attacked Tanjiro's family, he didn't only leave blood in Nezuko. He tried with the others, too, but they couldn't survive the transformation.

Demon blood, under certain circumstances, could be considered a lifesaving elixir. If someone on the verge of death could assimilate the blood, they would survive—but as a demon.

The boy's screams echoed as he writhed on the ground. After a long time, his cries faded. His severed right arm had regenerated, and his once-handsome face had turned pale, with his ears becoming pointed and black tiger stripes appearing on his face.

"Power. This is power." The boy's eyes gleamed with ambition as he felt the strength coursing through his body. He picked up his severed right arm's Nichirin sword. As he gripped the sword, its blade dulled, turning a grayish color despite its dark gold hue.

"Thank you, my lord." The newly turned demon boy knelt before the Upper Rank demon, the ambition in his eyes now replaced with apparent subservience.

At that moment, the sound of approaching footsteps could be heard. A dozen Demon Slayer Corps members arrived, quickly surrounding the Upper Rank demon and the kneeling boy.

"Kaigaku, are you okay?" The leader of the group asked, concerned. He hadn't realized the situation yet.

"Captain, something's wrong with him," one member pointed out, noticing Kaigaku's changed appearance.

"Ichinose, what a coincidence," Kaigaku said, standing up and facing the group. The Demon Slayers' expressions changed as they recognized Kaigaku's demonic features.

"Kaigaku, how could you?" The group was shocked and speechless. Despite Kaigaku's selfishness and arrogance, he was their comrade. They couldn't believe he chose to become a demon.

"Kaigaku, how could you betray Master Jigoro's teachings?" one member shouted angrily. According to Demon Slayer Corps rules, a mentor was held accountable for their trainee's actions and was required to commit seppuku if their trainee became a demon.

"The old man? Who cares? He always looked down on me and favored that coward. If not for his status as a former Hashira, I wouldn't have bothered acknowledging him," Kaigaku revealed his true nature. Trainees of former Hashira received special treatment, benefiting from their mentor's teachings and resources.

"You…" The surrounding Demon Slayers were stunned by Kaigaku's shamelessness.

"It's time to send you all to hell. Thunder Breathing, Fourth Form: Distant Thunder," Kaigaku declared, attacking the Demon Slayers. His attacks, ineffective against the Upper Rank demon, easily dispatched his former comrades.

Kaigaku's strength was already significant within the Demon Slayer Corps. If not for the full roster of Hashira, he would have been considered for the position.

As Kaigaku slaughtered the Demon Slayers who had come to assist him, the Upper Rank demon also made his move. With a forceful leap, he shattered the ground and attacked four crows flying overhead. Using his unique Moon Breathing and Blood Demon Art, he decimated three of the crows. The fourth, flying higher, managed to escape and flew away rapidly, evading the demon's reach.

This Upper Rank demon was none other than Kokushibo, the strongest of the Twelve Kizuki.

If it had been another Upper Rank demon, Kaigaku's pleas would have gone unheard, and he would have been killed. Upper Rank demons could create demons, but they only did so when intrigued by someone.

Kaigaku's pleas resonated with Kokushibo, reminding him of his past self, which is why he gave Kaigaku a chance.

"Where is the Demon Slayer Corps headquarters?" Kokushibo's six eyes focused on Kaigaku, directly asking. Muzan was troubled by the Demon Slayer Corps, and Kaigaku's transformation was an opportunity.

"I know, but a crow escaped. We must hurry, but it's just the two of us," Kaigaku hesitated. The Demon Slayer Corps' strength was formidable. Even though Kokushibo's power was overwhelming, Kaigaku doubted their success with just the two of them.

Kokushibo, confident but not foolish, understood Kaigaku's concerns. One-on-one, he feared no one, but being surrounded was a different story.

Kokushibo contacted their superior, and moments later, he and Kaigaku appeared in a mysterious building.

Muzan was extremely cautious, distrusting even his subordinates, especially the Upper Rank demons. Only he could contact them. For them to reach him, they had to go through Nakime in this mysterious building—Infinity Castle.

Nakime, created painstakingly by Muzan, lacked significant combat strength but could control the Infinity Castle and couldn't leave without Muzan's permission.

Muzan invested effort in creating Nakime for easy communication with demons. Without her, Muzan would have to personally locate the demons, a task beneath the Demon King.

With Nakime, a simple biwa play could summon any demon Muzan wanted, ensuring they never knew his exact location.

"We've found the Demon Slayer Corps headquarters," Nakime reported to Muzan, who soon appeared in Infinity Castle. Kaigaku, seeing Muzan for the first time, knelt, unable to lift his head. It wasn't just fear but the suppression from Muzan's blood.

"A crow escaped. Move quickly," Muzan ordered, and Upper Rank Two Douma and Upper Rank Three Akaza also appeared in Infinity Castle.

"Send them to the nearest location," Muzan commanded before leaving. Nakime's power required a demon at the target location for transportation, but the Demon Slayer Corps headquarters had no demons.

"I heard you almost got killed by the Demon Slayer Corps," Douma teased Akaza as they headed toward the headquarters.

"Next time, I'll reclaim my rank," Akaza retorted, ignoring Douma. Having survived decapitation, Akaza's power had increased, and he was determined to regain his former position, possibly even challenging Kokushibo.

"Confident, are we? Gained some new strength?" Despite knowing Akaza's power had grown, Douma remained indifferent.

Kokushibo, silent, led the way to the headquarters.

---

At the Demon Slayer Corps headquarters, the Butterfly Mansion, and the Ubuyashiki estate, many hidden members assisted in the relocation, following a contingency plan activated after the escaped crow's return. Their actions were orderly, having been trained for such scenarios. The Ubuyashiki family had long anticipated Muzan's search and prepared multiple safe houses.

Similar to the Swordsmith Village's swift relocation in the original story, the Ubuyashiki family had backup plans in place.

"Kaigaku betrayed us," several Hashira, including Daniel Davis and Kagaya Ubuyashiki, discussed their next move, lamenting Kaigaku's betrayal. Despite their disdain for his arrogance, his actions still saddened them, especially for his mentor, who would now have to atone.

The Thunder Breathing Hashira, called Roaring Hashira, now faced consequences for his trainee's transformation.

"Fight or retreat?" The group focused on the current crisis. With several Upper Rank demons expected to attack, the corps faced a severe threat. The recent encounter with Akaza demonstrated the difficulty of fighting Upper Rank demons.

"This could be an opportunity if Muzan appears. We could end this," Daniel mused. However, he knew Muzan would likely hide again if his strongest subordinates were defeated, prolonging the struggle.

Daniel realized they needed to lure Muzan out.

 In the original story, Kagaya Ubuyashiki sacrificed himself to draw Muzan out, a strategy they might have to consider again.

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