Isekai Adventure in the Dimensional Cube

It's uncertain how long it had passed before the roars that filled the training grounds finally subsided.

"Alright, let's take a break."

Reiger, seeing that many Demon Slayer Corps members had arrived at the training grounds, thought it over and still sheathed his sword, addressing the Pillars with that remark.

"Hah... Hah... Hah..."

The Pillars didn't have the strength left to respond, one by one collapsing onto the ground, gasping for air desperately.

"Damn it!"

Shinazugawa Sanemi gasped heavily, his face still filled with frustration.

"I still couldn't touch him even once today..."

Iguro Obanai also clicked his tongue in disappointment.

"The Master... is truly too powerful..."

Kanroji Mitsuri felt as if she was at her limits, just managing to sit on the ground like a duck, laboriously expressing her feelings.

"As expected of young Tsukiguni!"

Even Rengoku Kyoujurou, who was usually brimming with energy, couldn't get up now.

"Namo Amitabha..."

Himejima Gyoumei had stopped crying, sitting there grimy, murmuring chants of Buddha.

"Really, that guy is just too flamboyant..."

Uzui Tengen looked at Reiger with eyes that were different from before.

"... Monster."

Tokitou Muichirou lay there without caring for his image, softly uttering that assessment.

"..."

Tomioka Giyuu didn't want to speak, staring at the sky, seemingly deep in thought.

Even Kochou Shinobu heaved a sigh now.

"If only he had been born a bit earlier."

The statement from Kochou Shinobu was met with silence from the other Pillars.

They naturally understood what Kochou Shinobu meant.

"Indeed," Rengoku Kyoujurou said heartfeltly, "if young Tsukiguni had been born earlier, perhaps there would not have been so many tragedies."

"Kibutsuji Muzan surely can't be stronger than young Tsukiguni, right?"

Had this statement been made in the past, the Pillars would certainly not have simply conceded.

But now, they no longer thought the same way.

After all, for an entire week, they had besieged Reiger countless times, yet they had not even been able to graze the hem of his clothing, getting knocked to the ground time after time.

This was an assault by all nine Pillars!

The Demon Slayer Corps consisted of nine Pillars, all of them launching an attack on one person, yet not even touching a piece of his clothing—would anyone have believed it before?

Not to mention, they had now collectively activated their Demon Slayer Marks, except for Himejima Gyoumei, who had asked Reiger to remove it due to his old age to avoid imminent death. Although he had been fighting without his mark activated these days, Himejima Gyoumei was still one of the strongest members of the Demon Slayer Corps—even without the mark, he would not be weaker than the other Pillars who had activated theirs.

Such a group of nine Pillars, even if they were to attack Kibutsuji Muzan, might not defeat him, but surely they wouldn't fail to land a single strike, right?

At least, that's what the Pillars believed.

Yet Reiger had managed to keep all the Pillars from so much as touching him for seven consecutive days, repeatedly defeating them.

If such strength couldn't surpass Kibutsuji Muzan, then Muzan wouldn't be a demon but a god.

Of course...

"Don't get too optimistic,"

Reiger stepped forward and said just that.

"During the Warring States period, Tsukiguni Yoriichi was a Swordsman whose strength far exceeded Kibutsuji Muzan's, but didn't he also fail to kill Muzan and let him escape?"

What he meant was that winning was one thing, but whether or not you could kill was another matter entirely.

"Even I, facing Muzan who could explosively disintegrate himself into pieces and flee, can't guarantee that I won't let him get away. It's better not to cling to such illusions,"

Upon hearing these words from Reiger, the Pillars instantly became spirited.

"Then our esteemed Master, how strong do you think Kibutsuji Muzan truly is?"

Kochou Shinobu asked a question that everyone was concerned about.

The Pillars also wanted to know if they truly stood a chance against Kibutsuji Muzan with their current abilities.

However, reality was still cruel.

"Unfortunately, even if you all awakened to three types of powers and could solo the Upper Moon demons, whether or not you could defeat Kibutsuji Muzan working together is still an unknown,"

Reiger shared his view.

As for the strength of Kibutsuji Muzan, Reiger had a rough estimate.

The main basis for his estimate was naturally from the source material.

In the original source, as the Upper Moon One, Kokushibou was far superior to the average Upper Moon. He was capable of facing both Himejima Gyoumei, who had activated his Demon Slayer Mark and the Transparent World, and Tokitou Muichirou. Even with Shinazugawa Sanemi, who had also activated his mark, all three Pillars joining forces ended in one being killed before finally defeating him.

Such a Kokushibou, even by a conservative estimate, had the strength comparable to Lv.5.

While Kibutsuji Muzan, even after being affected by Tamayo's drug, faced off alone against Tanjirou, Himejima Gyoumei, Shinazugawa Sanemi, Tomioka Giyuu, Iguro Obanai, and Kanroji Mitsuri, a total of six people. These six either had their marks activated, had unlocked the Bright Red Sword, or had already entered the Transparent World. In the end, he was able to single-handedly suppress them all, leaving them with no option but to stall for time until dawn.

Just this performance alone was enough to prove that Kibutsuji Muzan was much stronger than Kokushibou.

Yet, Kibutsuji Muzan wasn't even at his peak in this state.

Firstly, hundreds of years ago, Kibutsuji Muzan almost got killed by Tsukiguni Yoriichi, and the sword wound from that time hadn't even healed, which weakened his strength somewhat.

Secondly, Kibutsuji Muzan was poisoned by Tamayo, with a compound drug containing four kinds of deadly poison that could affect him.

The first was a drug that could turn a demon back into a human.

The second was a drug that could age a demon continuously.

The third was a drug that could prevent a demon from splitting and escaping.

The fourth would destroy Kibutsuji Muzan's cells, after the first three drugs had taken effect.

In the final battle, Kibutsuji Muzan dissolved the drug that turned demons into humans, but the latter three drugs still affected him, preventing him from splitting and escaping, aging him by 9,000 years, and causing damage to his cells.

In such a state, if you couldn't say that Kibutsuji Muzan's strength was reduced to one-tenth, it was at least halved.

Still, Kibutsuji Muzan was able to fight the original protagonist and the five pillars without falling behind, which shows just how strong the Demon King must have been in his prime.

Kokushibou was already Lv.5, and Kibutsuji Muzan displayed better performance than him even with his power weakened, so at his peak, Kibutsuji Muzan, if not Lv.6, was probably not far from it.

"Thinking about it that way, Tsukiguni Yoriichi's strength is kind of terrifying."

Reiger muttered to himself silently.

A presumed Lv.6 Demon King almost got insta-killed by Tsukiguni Yoriichi's hands?

What level was Tsukiguni Yoriichi?

You could only say that he truly was the pinnacle of the Demon Slayer World, born with demon slayer marks, and understood the principles of breathing techniques and the world from a young age without any guidance, truly a bug-level cheat.

If someone like Tsukiguni Yoriichi were still alive, and like Reiger, could receive the blessing of the gods to fully develop their potential, he would definitely also be a freak capable of breaking limits, training basic abilities to the SSS stage.

Fortunately...

"Now I am not weaker than Tsukiguni Yoriichi."

Now Reiger, in his aggressive flow mode, had the strength equivalent to the lower end of Lv.7, and even compared to Tsukiguni Yoriichi at his peak, he would definitely not be inferior, possibly even stronger.

If Tsukiguni Yoriichi could insta-kill the prime Kibutsuji Muzan, there was no reason Reiger couldn't.

Even if Kibutsuji Muzan was Lv.6, what of it?

Reiger could have easily won against that level before evolving the Sun Breathing technique, let alone now.

But it was different for the pillars.

Even with their demon slayer marks activated and having access to the Transparent World, not to mention wielding Nichirin Blades that could cause significant damage to demons, the strength of a single pillar was, at most, only up to the limits of Lv.4.

Even Himejima Gyoumei, the pinnacle of the Demon Slayer Corps, after activating his demon slayer marks and the Transparent World, still didn't reach Lv.5, only just setting foot into it.

If Kibutsuji Muzan was the version from the later part of the original story, weakened several times, then the nine pillars might have had a chance to successfully hunt him down.

But if Kibutsuji Muzan really corresponded to Lv.6, could nine swordsmen, not even reaching Lv.5, possibly unite across two levels and succeed in their assault?

That would be quite a big question mark.

The pillars realized what Reiger meant, and each one frowned.

"Is Kibutsuji Muzan really that strong?"

Uzui Tengen asked himself, only to get an answer from Reiger.

"Having lived for a thousand years, even a mere pig could turn into a monster, let alone a ruthless and merciless Demon King," Reiger said. "Don't forget, the more humans a demon eats, the stronger they become, and as the first of his kind, who else in this world has feasted on humans more than Kibutsuji Muzan?"

You could only say that, under normal circumstances, no one in this world could win against Kibutsuji Muzan in terms of combat strength.

Tsukiguni Yoriichi, that was just a miracle.

"You want to join the fight, I'm not opposed, since you and the demons hold deep-seated grudges. I'm not you, I can't empathize, so I have no reason to stop you from killing demons."

"But I do not support you fighting Kibutsuji Muzan, risking your lives on a wager."

"It's unnecessary."

Reiger said to the pillars.

"Your adversaries are the Upper Moons, among which lie many demons with ties to you."

"They are the ones you should be vanquishing."

"As for Kibutsuji Muzan..."

Reiger turned around.

"He has long been mine."

Leaving these words behind, Reiger left the place.

All that was left were the pillars, watching Reiger's retreating figure, lost in deep thought.

...

"Tsuki, Tsukiguni sir!"

On the other side, as Reiger was about to leave the training field, someone called out to him.

"Hmm?"

Hearing this familiar voice, Reiger stopped in his tracks, turned around, and looked behind him.

There, someone was running towards him rapidly.

"Tanjirou?"

That person was none other than Kamado Tanjirou.