The space where the opponent resided was extremely vast and spacious, seemingly endless, giving the impression of having arrived at the world's end. Only a solitary throne sat atop it, and Muzan Kibutsuji was seated right above.
Roa licked his lips, gripping the two Nichirin swords at his waist, and walked toward him.
Muzan Kibutsuji was leisurely sitting on the throne, not speaking, merely resting with his right hand on his forehead.
However, the moment Roa stepped onto the stairs, Muzan Kibutsuji opened his cold, snake-like eyes, staring intently at Roa standing below. Muzan Kibutsuji spoke indifferently, "I didn't expect the Demon Slayer Corps to have grown so powerful without me noticing."
After a brief pause, Muzan Kibutsuji continued, "But these are just minor issues. Once I devour you, I will deal with that group one by one."
Roa revealed a mocking smile and said to Muzan Kibutsuji, "So confident? Don't break your teeth."
Muzan Kibutsuji ignored Roa's taunts and looked around, asking Roa, "Do you know where this is?"
Seeing that the other party wanted to waste time, Roa naturally did not rush to attack, and his aura gradually solidified.
Roa shook his head honestly, "I don't know."
Muzan Kibutsuji smiled, "This is the Throne, the deepest part of Infinity Castle. Be grateful for my mercy; I grant you a one-on-one challenge. Come closer; I can already smell your scent. Such a sweet aroma, mmm, quite nice."
After saying this, Muzan Kibutsuji rose from the throne, his plum-red eyes fixed on Roa.
He suddenly snapped his fingers, and Roa's space changed again. Roa's position began to stretch and shift, finally appearing opposite Muzan Kibutsuji.
At this moment, Roa could finally see Muzan Kibutsuji's appearance clearly. He was still dressed as before, but the difference was that his hair was no longer black but white.
Upon seeing the other party, Roa instinctively gripped the Kakutō at his waist, activating the Breath of Thunder rapidly, drawing his sword technique, and condensing his aura to the utmost.
Transparent World—Activate!
Sword Heart—Activate!
Magic flowed through his blood, and the dragon's blood began to boil at this moment, while his golden eyes lit up.
When Muzan Kibutsuji saw Roa at that moment, his originally indifferent expression gradually turned frenzied. He stared at Roa, murmuring, "I can feel it. As long as I devour you, my strength will surely advance further. Even without that legendary blue spider lily, I can overcome that annoying sunlight."
Roa calmly replied, "If you can do it, then try!"
The Kakutō suddenly unsheathed, and in an instant, Roa's figure transformed into a flash of lightning, a thunderous roar echoed as the lightning wrapped around the Kakutō, appearing before Muzan Kibutsuji in the blink of an eye.
Roa's goal was simple: to take the opponent's head.
With a full-force explosion, the thunder roared, and in an instant, the Kakutō slashed toward Muzan Kibutsuji's neck. Even though Muzan Kibutsuji was prepared, he was slightly taken aback by Roa's explosive speed.
But what of it?
Muzan Kibutsuji's handsome face gradually twisted into a grimace as he laughed, "Kid, don't be so impatient."
Suddenly, Muzan Kibutsuji's body began to change. His white hair, limbs, and lower body were enveloped in blood and hair, growing a massive mouth with sharp teeth all over his body. His arms transformed into thorny whips, striking fiercely at Roa.
Roa raised an eyebrow slightly, and the Kakutō was forced to change direction, slashing down at Muzan Kibutsuji's thorny whip. Although Muzan Kibutsuji's whip was powerful, it was not enough to contend with Roa's sword-drawing technique. In an instant, it was severed, and the Kakutō radiated intense heat, the severed end of Muzan Kibutsuji's whip sizzling as it was scorched by flames.
Roa's slash would not end so simply. With the enhancement of the Transparent World, Roa could see the opponent's vital points at a glance. The Kakutō was reversed in his grip, and another flash of lightning appeared, the lightning enveloping the Nichirin sword as it slashed directly toward Muzan Kibutsuji's chest.
Unfortunately, this strike had already been anticipated by Muzan Kibutsuji, who extended his left arm to form a flesh shield. The flesh buds on it squirmed, and Roa's Kakutō pierced into the flesh bud, emitting a sizzling sound. Roa looked at it, feeling a chill run down his spine.
This guy was even more perverse than Kokushibou. Upon closer inspection, the flesh buds on his arm were covered in countless "mouths."
Without further ado, Roa infused magic into the Kakutō, directly tearing apart the opponent's flesh shield.
Muzan Kibutsuji merely smiled slightly, the burned area quickly shedding its skin, and fresh green flesh buds sprouted, rapidly growing, and he even regrew his arms.
Muzan Kibutsuji chuckled, "How about it? Facing such a powerful me, do you still have a chance even now?"
Muzan Kibutsuji's response was simple; he could rely on his nearly immortal regenerative ability to engage Roa in a war of attrition.
Roa frowned slightly, but he still did not speak. He continued with the Breath of Thunder, still using the sword-drawing technique—Thunder, but this time, Roa took a bit longer to gather his strength.
This time, Roa's target was no longer Muzan Kibutsuji's head but his heart—specifically, the seven hearts in his chest.
Muzan Kibutsuji's structure could no longer be described as bizarre; he was a true aberration.
Roa realized that if he did not use the Breath of the Sun, even the Kakutō would not be able to inflict significant damage on him.
Reversing the sword of the Kakutō, lightning reappeared, and Roa's figure retreated explosively.
Muzan Kibutsuji raised an eyebrow and said, "What's wrong, kid? Are you preparing to surrender? If so, I can make it less painful for you."
Roa had no intention of engaging in banter with Muzan Kibutsuji. He reversed his grip on the sword, and the aura of the Sword God flowed out, revealing the temperament of the Sword King.
This time, Muzan Kibutsuji would definitely block. As long as he could pierce the opponent's heart the moment Muzan Kibutsuji blocked, it would be enough.
In the next moment, Roa moved.
Lightning enveloped Roa as he charged toward Muzan Kibutsuji's position, the Kakutō once again slashing toward Muzan Kibutsuji.
Muzan Kibutsuji snorted coldly, "Ignorant."
His arms grew again, but this time, it was not just his arms; Muzan Kibutsuji's torso began to change as well. His spinal cord elongated, and nine tubes extended from his back, each about four meters long.
This time, not only did his arms extend into thorny whips, but the nine tubes growing from his back also attacked Roa's position.
Compared to the thorny whips extending from his arms, the nine tubes behind Muzan Kibutsuji were the real trouble. The tubes pierced through the air, creating a series of sonic booms as they attacked Roa from all directions.
Such a speed-level attack, even with the Transparent World, would be difficult to react to immediately. However, for Roa, even such a swift attack was still not enough.
Roa transformed into an afterimage, disappearing, the lightning dissipating again. The Kakutō, wrapped in lightning, directly severed the three tail tubes attacking him, and Roa's figure suddenly accelerated, Muzan Kibutsuji's thorny whips missing their target. The severed ends fell to the ground, emitting a foul odor, blood splattering on the ground.
Without pausing, in almost an instant, Roa reappeared before Muzan Kibutsuji, delivering a powerful thrust to his chest.
Roa's thrust needed no further explanation; as the Sword King, this level of thrust was flawless.
The angle, posture, and timing were all perfectly aligned, simply inserting the sword into Muzan Kibutsuji's chest.
One of his hearts had been pierced, and the Kakutō, wrapped in intense lightning, was now dangerously close. Even if Roa wanted to escape, it would become extremely troublesome.
In a panic, Muzan Kibutsuji's face darkened as he realized that he had underestimated Roa. He had thought that in this form, he could kill Roa with a single strike, but he had underestimated his opponent.
What Muzan Kibutsuji did not know was that an even greater surprise awaited him.
The five tubes behind Muzan Kibutsuji attacked Roa again, while the recently severed arms had already regenerated, reaching for Roa's head.
Roa did not waste words and directly kicked.
Roa discovered that a kick always caused much more damage than a sword strike.
The powerful force knocked Muzan Kibutsuji to the ground, his body scraping against the ground as he tumbled away, kicking up dust and debris, and the surrounding structures were destroyed by Muzan Kibutsuji's figure.
Muzan Kibutsuji smirked, a sinister smile appearing on his face. The eight tubes at his tail firmly rooted themselves in the ground, halting his retreat. Muzan Kibutsuji looked up at Roa and said, "Kid, don't you know that you can use that person's sword technique? Why aren't you using it?"
Roa did not engage in idle chatter. He charged forward again, the Kakutō once more thrusting toward Muzan Kibutsuji's heart.
Muzan Kibutsuji roared, and the tubes behind him swung again, the air erupting with explosive sounds.
Roa remained expressionless as he sliced through the attacking tubes one by one. The severed tubes shattered on the ground, still writhing.
Continuously swinging his sword, the thunder roared, and Roa's speed increased. The speed of the Kakutō accelerated, and in the end, even Muzan Kibutsuji found it challenging to cope.
However, Muzan Kibutsuji's powerful regenerative ability gave him some peace of mind. No matter how rapid Roa's strikes were, he could not be completely killed. As long as the battle continued, he would maintain the upper hand.
As long as…
But in the next moment, the enveloping lightning began to change, flames ignited, and the sounds in his ears were no longer thunderous roars but the crackling of red flames.
Suddenly, Muzan Kibutsuji's pupils constricted, and his somewhat twisted face fixed its gaze on Roa.
What was that?
Memories began to overlap, the same posture, the same breathing technique.
Fear surged in Muzan Kibutsuji's heart. For three hundred years, since encountering that person, he had been haunted by that figure.
The scars left by that swordsman three hundred years ago had not faded even now. Beneath the surface of his skin remained the scars left by a man named Yoriichi Tsugikuni.
After fear came unparalleled rage. The one before him was not Yoriichi Tsugikuni; there was only one Yoriichi Tsugikuni. No matter how strong the boy before him was, he could not be compared to that one. He had realized this from their earlier exchange.
That's right, Yoriichi Tsugikuni was already dead; the person before him was just an imposter.
Thinking of this, Muzan Kibutsuji swung the eight tubes on his body toward Roa.
But the blazing flames erupted, and Roa's figure vanished like a bubble.
"Breath of the Sun, Fourth Form— Fake Rainbow." Roa's cold voice echoed from afar.
Muzan Kibutsuji's pupils suddenly constricted, and the eight tubes that had regrown swept out in all directions. Muzan Kibutsuji's attack range was extensive, and in such terrain, he could almost instantly cover the entire ground around him.
The ground was completely destroyed by the tubes transformed from Muzan Kibutsuji, mud and stones flying, revealing the underlying base layer, and dust rose. But this level of dust was inconsequential to both of them.
Suddenly, flames ignited in the distance, and Roa's voice rang out again.
"Breath of the Sun, Seventh Form— Sunflower Thrust Form."
Flames enveloped Roa's body, and circular flames erupted around the sword, continuously burning and raising the surrounding temperature once more.
The Kakutō in his hand turned an even deeper red, and Roa's figure accelerated again, his speed rivaling that of the Breath of Thunder.
The flames surged, the fire rapidly expanding from a distance, and the crimson Kakutō appeared before Muzan Kibutsuji in an instant.
Muzan Kibutsuji's pupils contracted as he attempted to recall the tubes behind him, but it was already too late.
The sword pierced into Muzan Kibutsuji's chest. This time, Muzan Kibutsuji's expression was no longer so indifferent. The sword, enveloped in flames, burned fiercely at the wound, the scorching heat radiating outward. Roa's speed was too fast; even Muzan Kibutsuji did not have time to react, only able to slightly shift the surrounding hearts.
Muzan Kibutsuji's small movement was naturally seen through by Roa. The Transparent World was not just for show, and since he had six hearts, piercing one was relatively simple.
The penetrating damage caused by the Radiant Burst instantly shattered Muzan Kibutsuji's heart. Unlike the damage from the Breath of Thunder, this time the damage was like a maggot burrowing into bone, continuously burning the organs surrounding Muzan Kibutsuji's body.
Roa acted swiftly, not hesitating, pulling out the crimson Nichirin sword that resembled flames, taking a deep breath as the surrounding flames ignited.
"Breath of the Sun, Sixth Form— Burning Bones, Summer Sun."
The blazing flames continued to burn, and Roa naturally connected to the next attack.
The flames surrounding the crimson sword spun continuously as Roa's strike once again approached Muzan Kibutsuji. This time, the target was no longer the opponent's heart, but rather their head.
Noticing Roa's intent, Muzan Kibutsuji was filled with extreme rage. His face was covered in bulging veins, and even his pupils were invisible, with his eyes entirely bloodshot.
"You brat, you will die!!!" Muzan Kibutsuji roared.
Suddenly, Roa's figure retreated rapidly, but it was already too late.
A terrifying shockwave erupted suddenly, centered around Muzan Kibutsuji.
It was a shockwave accompanied by thunder and lightning, a hurricane and explosions, indiscriminately bombarding in all directions.
As the shockwave spread, it destroyed everything around it. Even the Infinity Castle was completely obliterated by this violent shockwave, turning the already uneven ground into a terrifying wasteland.
Even the exposed foundations could not escape disaster; dirt flew, and everything around was reduced to ashes in an instant. This was as terrifying as an instant-cast holy-level magic.
The upper half of the entire building was completely blown apart by this strike from Muzan Kibutsuji, turning into nothingness.
At such close range, even Roa could not escape the extensive shockwave.
"Breath of the Sun, Second Form: Clear Blue Sky."
Roa's expression tightened as he gripped the crimson sword. His heart raced violently again, and the Nichirin Sword transformed into a circular vertical slash, presenting a circular flame that danced. The firelight enveloped Roa's body, intertwining with the sound waves generated by the explosion, creating a series of explosive booms.
But this was not the end; merely resisting the opponent's shock was not enough, and Roa's expression remained grave.
This shockwave was not just an extremely powerful physical force; it also carried a series of negative buffs that could disrupt the entire nervous system, causing spasms and rendering a person immobile, leading to death.
Even though Roa tried to use the Breath of the Sun's Second Form: Clear Blue Sky, the residual waves from the explosion still grazed his left arm. Just this small abrasion made Roa feel a tingling numbness in his left arm.
And this was while in the Dragon Blood state, where Roa's resistance to such negative effects was already at a considerable level. Yet even so, the shockwave released by Muzan Kibutsuji still affected Roa.
"Is this the legendary enchanted attack? No, it should be Muzan Kibutsuji's Blood Demon Art." Roa smirked, his right hand still firmly gripping the crimson sword.
As the Sword King, as long as the sword remained intact, this minor injury was not a problem at all.
This was Muzan Kibutsuji's Blood Demon Art, his trump card, his strongest attack method.