When Shinobu Kocho, Tengen Uzui, Mitsuri Kanroji, and Obanai Iguro arrived, all they saw in the courtyard was a roaring serpent of fire completely consuming Upper Moon Three.
"Is that... Flame Breathing?"
Shinobu stared at the blaze that seemed poised to burn everything to ash, frozen in place.
A few seconds later, the flames receded, leaving behind only scattered chunks of flesh dissolving on the ground and a long, deep fissure carved into the earth by a Nichirin Blade.
And who else could the true form hidden within that serpent of fire be but Sukuna?
Sukuna raised the Nichirin Blade in his hand. The blade was now entirely crimson, as though freshly pulled from a forge, but this state didn't mean reduced performance. On the contrary, this condition—known as the Red Blade—was a lethal weapon against powerful demons, capable of suppressing their regeneration.
Sukuna had entered the Red Blade state completely unconsciously. It was purely a result of his body, adjusted by cursed energy, approaching the conditions for awakening a Mark. His body temperature and grip strength both far exceeded the requirements for activating the Red Blade.
Sukuna had also noticed it when he struck Akaza moments ago. In this state, the damage inflicted by the Nichirin Blade seemed uniquely effective against demons. He could sense that the demon's usual passive, ever-active regeneration had momentarily failed.
Sukuna could more or less understand it. This likely stemmed from the unique properties of the Nichirin Blade's material, combined with the heat enhancement from the Mark-like state, which amplified its demon-killing potency.
Still, the effect was limited. If Sukuna himself were a demon and encountered this situation, he would simply expand dismantle over his own body. Using it's slashes, he would directly excise the wounds caused by a Red Blade in this state, nullifying its effect and allowing his demonic regeneration to function freely.
He internally assessed the situation. This seemed like something the Marked Swordsmen could potentially master through training. And with that cockroach-like numerical advantage, combined with this blade-heating ability, it might not be entirely impossible for them to seriously injure an Upper Rank demon.
But even so, Sukuna felt it wasn't enough. This only brought them to the edge of being able to fight back. He still hadn't faced Upper Moon Two, Upper Moon One, or Muzan himself in battle. He couldn't gauge their true strength.
Sukuna still sensed that something was missing in this thousand-year conflict between swordsmen and demons. Some missing puzzle piece that had shaped the current stalemate. Had some single individual turned the tide?
The thought surfaced in Sukuna's mind for some reason, but he quickly dismissed it. Humans were too short-lived. They probably couldn't have caused such far-reaching effects.
"..."
Shinobu hadn't expected events to unfold like this. Sukuna had just told Upper Moon Three to fight them, and then he personally slew Upper Moon Three instead.
The other Hashira remained silent as well. Tengen Uzui and Obanai Iguro separately checked the injuries of Muichiro Tokito and Gyomei Himejima.
But unfortunately, their injury assessment had effectively become a cause-of-death determination. The wounds on both bodies were clearly caused by fists and feet, not cuts or Nichirin Blade slashes.
This also confirmed to the Demon Slayer Corps that Sukuna hadn't killed them—Akaza, Upper Moon Three, had. They even suspected Sukuna might have only intervened because the two were killed...
But under the circumstances, none of them dared to ask Sukuna directly. They also noticed that the deceased Muichiro Tokito had already awakened a Mark on his body.
Even on Sukuna's body, among those orderly patterns of cursed markings, there seemed to be a Mark as well. Just as Shinobu gathered her courage to speak.
"Um, Lord Sukuna..."
Sukuna didn't respond. Instead, he spoke to himself.
"Oh? Here already?"
"Who? Are you talking about us?" Shinobu thought for a moment that Sukuna meant them, but the fact that he never once looked in their direction made it clear he wasn't referring to them.
What Sukuna was actually referring to were the Upper Ranks following the signal of Akaza's death to the scene.
The two Upper Ranks who arrived, Gyokko and Hantengu, could tell immediately from the atmosphere that Sukuna was the strongest presence there. Even now, he still reeked of the blood of Upper Moon Three Akaza and Muzan himself.
The reason Gyokko and Hantengu were respectively Upper Moon Four and Upper Moon Five wasn't that they didn't want to climb higher to become Three, Two, or One—it was that they couldn't. They couldn't even beat Upper Moon Three Akaza.
Sukuna casually glanced at the two.
"Seriously. If I'd known killing one Upper Rank would make the others swarm me like insects, I should've just killed him from the start."
Gyokko and Hantengu naturally caught the contempt in Sukuna's words.
Without exchanging a word, both demons simultaneously felt their wariness of Sukuna spike. They sensed this guy was terrifying—not just strong, but on another level.
So their response was very simple. Following Muzan's original instructions, they instantly transmitted their location coordinates to Muzan through their shared consciousness.
Inside the Infinity Castle, Muzan received the image of Sukuna through Gyokko and Hantengu's eyes. He let out a manic laugh, fury and excitement intertwined.
"HAHAHAHA! Finally found you, you bastard!"
Muzan didn't forget to transmit the information, along with the location data, to Nakime standing not far behind him.
Nakime, not yet promoted to Upper Moon Four at this time, naturally understood what she needed to do upon receiving this information from Muzan. She quietly plucked her biwa's strings and activated her Blood Demon Art.
Almost simultaneously, Sukuna faintly heard the sound of a biwa and was drawn to the wooden door that appeared beneath his feet.
But the moment the door opened, instead of being pulled into the Infinity Castle, Sukuna leaped high into the air while stroking his chin and observing what lay beyond.
Through the doorway, Sukuna saw a vast, brilliantly lit space constructed from an enormous number of wooden buildings.
And for such a massive space to exist directly beneath the Demon Slayer Corps' headquarters—there was no way the Corps could have lasted a thousand years. They likely would have been annihilated in a single night.
Which meant only one answer. This was another Blood Demon Art related to space manipulation. Sukuna almost couldn't help but remark on how many spatial abilities he'd encountered in this world already.
"Seriously. You want me to go in that badly?"
Sukuna spoke while watching Gyokko and Hantengu leap toward him simultaneously, clearly intending to drag him into the Infinity Castle.