Isekai Adventure in the Dimensional Cube

Demons have their elites named the Twelve Demon Moons, divided further into Upper and Lower Moons, clearly delineating their strength and rank.

The Demon Slayer Corps follows a similar notion, with ranks based on status and varying strengths.

The Ghost Hunters belonging to the Demon Slayer Corps are generally classified into ten grades from A to J, with A being the highest and J the lowest. The higher the grade, generally the stronger the member is and the better their treatment, status, and influence within the corps.

However, class A isn't the highest rank within the Demon Slayer Corps.

The Demon Slayer Corps has one leader and nine Pillars.

The leader commands the entire Demon Slayer Corps.

The Pillars are nine highly revered swordsmen who support the Demon Slayer Corps and are stronger than anyone else within the corps.

They are named after the breathing styles they use.

For instance, the world's five basic breathing techniques—Flame, Water, Wind, Thunder, and Stone. The Pillars who master these techniques to the pinnacle are named after the breathing style they have mastered.

The Pillar who uses Flame Breathing is known as the Flame Pillar.

The Pillar who uses Water Breathing is known as the Water Pillar.

And so forth—thus the nine Pillars each bear the name of their respective breathing style.

Rengoku Kyoujurou, this most distinctive Ghost Hunter, is the Flame Pillar among the nine mightiest swordsmen in the Demon Slayer Corps.

Simultaneously, he is also the most admirable and poignant swordsman who is about to engage in a fateful battle with an Upper Moon demon on this Infinite Train, an encounter that will inevitably conclude.

Reiger then turned his attention toward the man, who illuminated the dark all around him like a flame.

"Hmm? What is it, Bento Boy?"

While devouring his bento, Rengoku Kyoujurou, for some reason, addressed Reiger with a unique nickname, evidently noticing that Reiger's bento was from the same shop as his.

"Surely you're more of a Bento Boy, no, it should be Bento Young Man."

Unable to resist, Reiger retorted but did not dwell too much on the topic and instead smiled at Rengoku Kyoujurou.

"Since someone like you has boarded this train, it seems this train is bound to encounter trouble soon."

Reiger's words slowed down Rengoku Kyoujurou's pace of eating his bento.

"Yes! It seems Bento Boy you know quite a bit about our affairs!" Rengoku Kyoujurou seriously nodded, his smile undiminished, said, "But rest assured! With me here, everything will be swiftly resolved!"

Rengoku Kyoujurou, speaking in such a loud voice, indeed attracted more than just a few stares.

But since he himself didn't care about being overheard, Reiger cared even less.

"There are two hundred people on this train, can you really handle them all?"

Reiger continued eating his bento as well, looking ahead as he spoke.

"Yes! It will probably be very difficult, right?"

Rengoku Kyoujurou openly admitted this point without any evasion.

Although he was a Pillar, one of the mightiest nine swordsmen of his time, fighting demons while protecting two hundred lives was no ordinary task indeed.

If the opponent were an average demon, that would be one thing.

A common demon, in front of the Flame Pillar, was merely a matter of one strike.

Even a Lower Moon among the Twelve Demon Moons would not match a Pillar of the Demon Slayer Corps.

You see, there are two criteria to become a Pillar in the Demon Slayer Corps.

One is to slay fifty demons.

The other is to subdue a member of the Twelve Demon Moons.

Thus, most Pillars in the Demon Slayer Corps have personally defeated a member of the Twelve Demon Moons, and though only the Lower Moons, it still sufficiently demonstrates their strength.

But already, more than forty people have disappeared on this Infinite Train. If they have been devoured by demons, then the nemesis is certainly not ordinary.

Just as humans gain nutrition from eating meat, demons grow stronger by consuming humans.

The more people they eat, the stronger the demons become, and the stronger the demon, the more humans they can consume. Ordinary demons might not even manage to devour such a large number of people.

Yet the Infinite Train has already "consumed" over forty individuals. This kind of consumption rate suggests that the demon appearing here must at least be a Lower Moon.

Rengoku Kyoujurou certainly does not fear a Lower Moon, but to combat a Lower Moon while protecting the lives of two hundred people is no simple task.

Moreover, what if the demon appearing on this Infinite Train is not a Lower Moon, but an Upper Moon?

The Upper Moons, six demons second only to the Demon King, have not changed their ranks or been subdued in nearly a hundred years. They have even counter-attacked and defeated several Pillars from the Demon Slayer Corps in the past. Their strength is not comparable to that of Lower Moons.

If an Upper Moon has appeared here, Rengoku Kyoujurou might not even be sure of his own safety, let alone protecting others.

However—

"Even then, I will fulfill my duty and not let a single life be lost in front of me!"

Rengoku Kyoujurou clasped his arms across his chest and shouted loudly at the train's ceiling.

"You all can rest easy!"

This declaration startled all the passengers in the carriage.

Eventually, only Reiger and Rengoku Kyoujurou were left in the entire carriage.

To others, Rengoku Kyoujurou, who had been shouting and saying inexplicable things, must have seemed no different from a madman.

Only Reiger, from these loudly spoken words, sensed a powerful, resilient strength.

This man genuinely thought this way, thinking not to let anyone lose their life in front of him.

Even if the ghost that was about to appear were an upper-rank ghost, he would fight until the end to protect every person on this train, right?

Those who felt the power in his words probably felt reassured as he had said.

But Reiger watched the man and simply said one line.

"You're here to protect everyone here, but who will protect someone like you?"

A casually uttered sentence, but it made the assertive Flame Pillar unexpectedly freeze.

He didn't know that Reiger also spoke with emotion.

After all, in the original story, Kyoujurou did manage to ensure not a single one of the two hundred people on the Infinite Train died, but in the end, he lost his own life.

Reiger genuinely admired the Flame Pillar's actions, which is why he said that sentence.

Unaware of all this, Kyoujurou gazed at Reiger for the first time, looking at the youth in front of him eating the same type of boxed lunch and smiled.

"The responsibility of those born strong is to protect the weak, not to use gifts bestowed by heaven to harm others or accumulate personal wealth."

Kyoujurou's voice was as loud and forceful as before.

But this time, his voice contained not only strength but also conviction.

"Protecting everyone here is my responsibility."

And what about himself?

"Where there's responsibility, there's conviction, how does danger even matter? Stand firm and forge ahead!"

Kyoujurou patted his own chest and burst into hearty laughter.

"Don't underestimate me, boxed lunch boy, my spirit can burn too!"

Burning spirit, moving straight ahead.

This is what makes a Flame Pillar.

"......"

Reiger didn't speak again but silently continued eating his boxed lunch, until the last bite.

Then, he placed his finished lunch down, adopted the etiquette of this world, and pressed his hands together.

"Thank you for the meal."

After all was done, Reiger turned toward Kyoujurou.

"The responsibility of those born strong is to protect the weak, right?" Reiger looked intently at Kyoujurou and suddenly smiled, saying, "In that case, my responsibility must be to protect you then, right?"

"What?" Kyoujurou was taken aback.

"Isn't it?" Reiger smiled and said, "After all, I am stronger than you."

Reiger's statement was unusually calm and indifferent, entirely unlike Kyoujurou's loud, powerful tone.

But it was this peaceful statement that gave Kyoujurou an unbelievable sense of security.

"Stronger than me…?"

Kyoujurou murmured softly, then broke into a broad smile.

It was like sunshine, like flames, fierce and sunny.

"What an incredible young man," Kyoujurou said with a laugh: "But unfortunately, I am a million times stronger than you think, so let me protect you!"

"No, no, no, I think I am a hundred thousand times stronger than you think," Reiger insisted earnestly: "So let me protect you."

"Then I am a million times stronger than you think! Let me protect you!"

"Then I am ten million times stronger. It will still be me protecting you."

"Then I am a hundred million times stronger!"

The two continued this bizarre argument in the empty train car, prompting bewildered expressions and a spontaneous urge to smile inexplicably.

As the argument progressed, a third voice suddenly burst in, overruling them both.

"This lord is ten billion times stronger than you all! If you don't believe it, let's settle this with a duel!"

Accompanied by such a high-pitched shout, at the empty train car door, a figure charged from behind the glass at high speed.

"Pig Assault!"

Shouting so, the figure broke through the train car door, bringing with it countless splinters, and charged into the car holding Reiger and Kyoujurou.

"Stop it! You stupid pig!"

"Calm down! Inosuke!"

Upon closer inspection, there were actually two other people clinging to this charging figure, their faces a picture of despairing attempts to stop him, yet completely ineffectual.

And the one who had broken in was someone with a… well… boar's head?

"Hahaha! Where's the Flame Pillar? Let's have a duel!"

The boar-headed individual said, laughing loudly with his hands on his hips.