Having reached a conclusion, Sukuna stopped paying attention to the battle between Akaza and Tokito Muichiro and Gyomei Himejima. He stood in place and continued thinking.
Muichiro glanced at Sukuna, who appeared deep in thought, confirmed that he truly had no intention of acting, and then resumed his attack on Akaza.
"Mist Breathing: Seventh Form: Obscuring Clouds!"
With his newly awakened Mark, Muichiro's figure dispersed like true mist within the dust kicked up by his movement.
This was not an afterimage of high-speed motion. His presence and form had nearly completely blended into the environment, vanishing in an instant.
The next moment, he appeared before Akaza with impossible speed, his blade aimed precisely and swiftly at the relatively weaker defense of Akaza's waist.
Even Akaza was shocked by the drastic improvement in Muichiro's ability. Just by manifesting those strange markings, this slash was more than twice as fast as before.
He was forced to turn and deal with Muichiro first. That decision gave Gyomei a brief moment to catch his breath.
"Aaaaaaaaaah—!" Gyomei, his body now covered in wounds, roared like a beast on the verge of death, pouring every ounce of his remaining strength into that final cry.
Gyomei knew very well that with his current injuries, there was no chance of survival. He would not even need to wait for the Mark's backlash to claim his life.
Even if by some miracle he lasted until the battle ended, the Demon Slayer Corps' medical treatment could not save him. And Gyomei certainly did not pin his hopes on Sukuna healing him.
Given how many Hashira had died brutally at Sukuna's hands, Gyomei considered himself fortunate to have received even one treatment from him.
He also knew that without his specially made Nichirin blade, even if he survived, he would be of little use for a long time. So he decided to sacrifice himself, using his own death to create an opening for Muichiro to kill Akaza.
Akaza, naturally able to track Gyomei's movements through his fighting spirit, made a quick decision in the face of Muichiro's slashes.
"Technique Extension: Final Form: Blue Silver Chaotic Afterglow!"
Akaza pivoted sharply, using himself as the center, and unleashed over a hundred punches simultaneously at Muichiro on one side and Gyomei on the other. The fists were like streaks of light.
That barrage of fists was something Muichiro, locked in his attacking motion, could never hope to block.
On the other side, Gyomei's situation was even worse. Even with Transparent World, his shattered body could no longer evade.
Thud thud thud!
The sickening sound of bones breaking rang out repeatedly. Even though Gyomei had completely ignored his body's pain signals, his fractured spine could no longer bear his weight. Gyomei collapsed half a meter before Akaza, lifeless.
On the opposite side, Akaza had given Muichiro special attention. His fist drove brutally into Muichiro's right chest.
The boy's body, like a broken doll, was sent flying once again. Blood traced a graceful arc through the air.
...
Sukuna had already begun adjusting his own body to replicate the state Muichiro had just achieved. With his level of bodily control, this was effortless.
And as he had expected, as he raised his heart rate past two hundred beats per minute and simultaneously raised his body temperature past forty degrees, he could genuinely feel the power flowing from his heart.
Even without a mirror to see his full appearance, he could perceive the subtle changes in his body, along with the burden and backlash that accompanied that power.
Given Sukuna's past experiences, he had rarely needed to push himself to his limits and squeeze out every ounce of his body's strength. So he found this backlash rather novel.
After all, Sukuna had eaten his own twin when he was a mere fetus. His identity as a powerful being was essentially innate.
Even his loss in that final battle in Shinjuku was due to the strain of fighting Gojo Satoru combined with the backlash from Megumi Fushiguro, the vessel he inhabited. It was not due to exhausting his own cursed energy reserves.
But the Mark's side effects, which were nearly insurmountable for the swordsmen of this world, were utterly trivial to Sukuna.
The mild, continuous backlash could be completely neutralized with Reverse Cursed Technique. By periodically and continuously applying Reverse Cursed Technique, the Mark became essentially harmless. The Mark, for Sukuna, was simply a way to exchange cursed energy for greater physical enhancement.
It was not that Sukuna could not achieve this level of enhancement with cursed energy alone. From a results perspective, that was entirely possible.
It was simply that, as a completely independent power source, the energy consumption was much smaller than purely using cursed energy to reach the same level. It gave him an additional option, and it was somewhat interesting.
In fact, Sukuna's successful awakening of the Mark had something to do with the body he currently inhabited, though he did not know this and had no way of knowing it at the time.
But after personally experiencing the Mark, combined with his understanding of Upper Moon Three Akaza's abilities, Sukuna felt that the Mark alone should not have allowed the Demon Slayer Corps to contend with demons for a thousand years.
After all, neither Gyomei nor Rengoku Kyojiro, even with their Marks awakened, could have defeated Akaza alone. And even the two of them together would likely have paid a heavy price to do so.
Did the Breathing Technique swordsmen possess some other means specifically targeting demons?
Or was there some hidden circumstance he did not know about?
The more Sukuna thought about it, the less he understood why demons had been held back by mere humans. Under normal circumstances, with their overwhelming power, demons should have conquered all of Japan long ago. Especially a thousand years ago, when conditions were far more primitive, which should have worked in the demons' favor. Sukuna genuinely could not figure it out.
Sukuna glanced down at Muichiro, who had flown to his feet. The boy's pupils were already glassy, blood seeping from all seven orifices. He then looked toward Akaza and spotted the corpse of Gyomei at his feet.
This outcome matched Sukuna's earlier prediction. A swordsman who had lost his weapon and could not properly execute his Breathing Techniques was essentially useless. The other, having just awakened his Mark, was only on par with that same swordsman in strength. There was no way they could win.
Sukuna felt that since he had already mastered the Mark, there was no need to wait for the remaining swordsmen to come and throw their lives away against Akaza. He had nothing better to do anyway, so he might as well use Akaza as a test subject to see how much power he had gained with the Mark.
Thinking this, Sukuna slowly drew the Nichirin blade from his waist. In that moment, in Akaza's eyes, the fighting spirit radiating from that blade shone as brightly as the moon in the night sky.