Isekai Adventure in the Dimensional Cube

"Ha... ha... ha..."

Unconsciously, within the unfinished training ground, all the flashes of blades and booming noises had vanished, leaving only the sound of rapid breathing echoing through the air.

A group of Pillars, who could typically maintain steady breathing even in their sleep, had perfected their breath control to the utmost limit, almost never allowing their breathing to become erratic, yet at this moment, they found themselves gasping uncontrollably.

"Two hours, huh?"

Reiger estimated the time and realized that the Pillars had been fighting intensely for a full two hours without any break.

No wonder even these masters of breath control couldn't help but pant after two hours of continuous fierce fighting.

Especially Rengoku Kyoujurou and Shinazugawa Sanemi, these two were already lying on the ground, unable to get up.

Seeing this, Reiger finally called a halt.

"Let's stop here," Reiger said. "It seems my guess was right, unlocking the marks is no easy feat at first."

Upon hearing this, the Pillars propped themselves up, struggled to stabilize their breathing, and then gathered around Reiger.

"So what do we do?" Uzui Tengen said, his head drenched in sweat as he pushed his hair back, "We did as you suggested, fought an incredibly flashy battle, yet we still couldn't unlock the marks. It wasn't all in vain, was it?"

"It definitely wasn't," Kyoujurou, still catching his breath, said loudly, "Even if we didn't unlock the marks, putting effort into combat training like this has to be meaningful!"

"It's the marks, Mr. Rengoku," Kanroji Mitsuri said, too exhausted to even hold up her arms, clutching her stomach with a pitiful look, "We've been fighting for so long, I'm getting hungry."

"Just hold on a little longer," Iguro Obanai whispered, "It's almost lunchtime."

"Tch," Shinazugawa Sanemi tightened his grip on his sword and, with a look of discontent, turned his head to look at Himejima Gyoumei and said, "Himejima, you're up next with me."

"Amitabha," Himejima Gyoumei, probably the best in shape among the Pillars, seemed not to have sweat a single drop as he responded, "The Wind Pillar is right, if it doesn't work once, we have to keep going. We can't give up because of one failed attempt."

"That's also true," Kochou Shinobu sighed, brushing off the dust from her body, "Although it's not exactly rehabilitative training, since I've been seriously injured before, it's better to keep this body moving. I don't want to face a gruesome defeat against an Upper Rank demon again."

"...Same here," Tokitou Muichirou said indifferently, "I don't want to be powerless again if our master faces danger next time."

The Pillars all expressed their determinations, lifting the somewhat dampened spirits once again.

"Then next is my turn..."

Tomioka Giyuu, as if timing his moment perfectly, prepared to find teammates.

However...

"Mitsuri, how about we spar next?"

Kochou Shinobu extended an invitation to Kanroji Mitsuri.

"Yeah yeah! I'd love to!"

Kanroji Mitsuri, naturally not refusing, happily accepted.

As the only two women among the Pillars, Kochou Shinobu and Kanroji Mitsuri got along well. Shinobu would sometimes ask Mitsuri for cooking tips, and so the two were considered close friends.

"Uzui, let's have a match."

Iguro Obanai also invited Uzui Tengen.

"Alright! Although snakes aren't very flashy, your eyes are! Let's have a spectacular fight!"

Uzui Tengen was quite interested in Iguro Obanai's invitation, and without a second thought, he accepted immediately.

The Sound Pillar, who liked flashy things, might not be particularly fond of the Snake Pillar's somber personality, but Iguro Obanai's heterochromic eyes seemed to have hit the right spot with him.

"Then it's just us now, young Tokitou. I look forward to it!"

Kyoujurou Rengoku turned to Tokitou Muichirou with a bright smile.

"Hmm."

Tokitou Muichirou also seemed to have a good impression of Rengoku Kyoujurou, and his expression relaxed considerably.

And so, the teams were successfully formed once more.

Tomioka Giyuu: "..."

Our Water Pillar managed to end up alone again.

Nevertheless, just as the Pillars were about to embark on another round of intense combat, suddenly, something happened.

An overwhelming presence burst forth from Reiger, causing the Pillar's expressions to change abruptly.

"Tsukiguni Yoriichi?"

"Yoriichi?"

Rengoku Kyoujurou and Kochou Shinobu were both astounded.

"Hey!"

"Whoa whoa whoa! What's going on?!"

Shinazugawa Sanemi couldn't help but shout at Reiger, and Kanroji Mitsuri was also thrown into panic.

The rest of the Pillars, to varying degrees, showed expressions of shock as they looked at Reiger, their eyes full of astonishment.

Reiger, with his eyes closed, emitted an astonishing heat from his body, causing the temperature of his skin and the rhythm of his breathing to change.

"Breath—Inhale—"

Reiger regulated his breathing, his chest pumping like bellows.

In this state, the Pillars could clearly hear Reiger's heartbeat.

That heartbeat was becoming more intense, quicker, and, combined with the rising body temperature of Reiger, gradually, dark lines began to form on his forehead.

Yes.

Reiger had unlocked the marks.

The pillars, having witnessed this spectacle, were incredibly shocked and bewildered.

Only when Reiger stabilized his breathing did he open his eyes and look at his own hands.

"So this is the mark," Reiger muttered to himself, "Indeed, it is quite an interesting power."

Hearing these words, all the pillars finally snapped out of their shock and bewilderment.

"What are you doing?" Uzui Tengen said in disbelief, "Do you have a death wish?"

Earlier, Reiger himself had said that due to side effects, he was reluctant to activate the mark.

But now, he suddenly activated the mark, unleashing a power that was said to prevent one from living past 25 years of age—how could this not provoke such a reaction from Uzui Tengen?

Not only Uzui Tengen, but all the pillars were puzzled and moved by Reiger's actions.

Especially Rengoku Kyoujurou and Kochou Shinobu, who were relatively close to Reiger; their faces now held a trace of urgency.

"Foolish! Young successor of the nation!"

Rengoku Kyoujurou shouted loudly.

"Successor of the nation..."

Kochou Shinobu's gaze towards Reiger was also quite complex.

Reiger lowered his hands and raised his head to look at the pillars who were astonished, confused, or incredulous, his expression unusually calm.

"It's now fairly certain that the first person to activate the mark should ideally be a user of the Breath of the Sun," said Reiger, "At the very least, users of the Breath of the Sun tend to awaken the mark more easily when there is no marked swordsman present."

A moment ago, Reiger had managed to raise his body temperature to 39 degrees Celsius using the power of the evolved Breath of the Sun and also adjusted his heartbeat with breathing techniques, increasing it to more than 200 beats per minute, and as a result, directly activated the mark.

This was enough proof that the first person to activate the mark was most likely to be a user of the Breath of the Sun, or perhaps only the users of the Breath of the Sun could become the initial person to activate the mark.

In the original narrative, Tsukiguni Yoriichi naturally possessed the mark, and after joining the Demon Slayer Corps, he inspired the other swordsmen to awaken their marks in succession. And when Tsukiguni Yoriichi left the Demon Slayer Corps, after the death of all marked swordsmen, no new awakenings of the mark occurred among them.

In the original plot, the pillars of the Demon Slayer Corps also managed to activate their marks only after Tanjirou had awakened his. Until that point, no matter how fiercely they fought demons, even to the point of sacrifice, there was no sign of their marks being activated.

For example, Rengoku Kyoujurou died in the hands of Akaza during the incident on the Infinite Train in the original story.

Their fierce battle lasted from night to dawn, and from dawn until the sun rose. Rengoku Kyoujurou even fought desperately at the end, paying with his life to drag Akaza into daylight. After such an intense battle, had Rengoku Kyoujurou not raised his body temperature to 39 degrees, or his heartbeat to over 200 beats per minute?

Impossible.

Rengoku Kyoujurou was a user of the Flame Breathing, and for him, raising body temperature during battle was commonplace, and his heartbeat becoming intense under the enhancement of breathing techniques that strengthened his cardiorespiratory function was likewise not unusual.

Yet, such a Rengoku Kyoujurou did not awaken a mark. Instead, the rest of the pillars easily awakened theirs after Tanjirou's mark was activated—could this not explain everything?

With this in mind, having seen that the pillars could not awaken their marks through the means mentioned in the original narrative, Reiger began to suspect...

"If there isn't a user of the Breath of the Sun to activate the mark first and induce the awakening around others, then I fear none of you will succeed in awakening a mark."

Reiger said this as he touched his forehead, addressing the pillars.

"Now, you can try again to see if you can activate the mark."

Upon these words, the pillars fell into silence one by one.

Even Shinazugawa Sanemi and Iguro Obanai stared intently at Reiger, their eyes filled with complex emotions.

Seeing this, Reiger spoke up to correct them.

"Don't misunderstand; I didn't choose to activate the life-shortening mark for your sakes," said Reiger, "I have a way to remove this mark, so don't overthink it."

The pillars were stunned.

"Is that true? Young successor of the nation!"

Rengoku Kyoujurou promptly asked.

"True."

Reiger nodded.

He wasn't lying.

After all, Reiger's Decomposition Magic possessed an abstract property that allowed it to break down not only matter but even magic itself.

Such Decomposition Magic, if applied to the mark, should be feasible, right?

Even if it wasn't, it didn't really matter.

"After all, what arrived through Dimensional Travel is just a materialized consciousness; even if it dies, it only ends this episode of Dimensional Travel and doesn't harm the original entity. As long as I'm not activating the mark in the land of Akasha, it shouldn't affect the lifespan of the original entity," Reiger thought to himself.

With such reasoning, Reiger had chosen to activate the mark in the presence of the pillars.

With his mark activated, the pillars should be able to awaken their marks quickly, right?

Everything that followed seemed to naturally fall into place.

As it turned out, Reiger's hypothesis was correct.

After his mark was activated, the pillars once again raised their body temperature to 39 degrees and their heart rate to over 200 beats per minute, and they finally began to successively awaken their marks.

"It worked!"

Shinazugawa Sanemi clenched his fists and let out a loud shout.

On his right cheek, a green windmill pattern appeared.

That was his mark.

"...It actually worked."

Iguro Obanai looked at his left hand, which now had a purple snake-like pattern extending to his left face.

"Is this the mark?"

Tokitou Muichirou touched his face, from his left forehead to his right cheek there was a cloud-like pattern.