Isekai Adventure in the Dimensional Cube

Ubuyashiki Kagaya, this was the name of the man facing imminent death before Reiger's eyes.

He was the Family Head of the Ubuyashiki family, the 97th leader of the Demon Slayer Corps, and the current leader.

The members of the Demon Slayer Corps, whether they were Pillars or regular slayers, all held this leader in high esteem and respect, addressing him as Lord.

Now, this leader of the Demon Slayer Corps, with the assistance of his wife and a pair of daughters, was walking out from the mansion to stand under the sun, facing Reiger.

"Welcome to the headquarters of the Demon Slayer Corps, Mr. Tsukiguni Yoriichi,"

said Ubuyashiki Kagaya with a gentle tone and a peaceful expression, greeting Reiger.

"I apologize for not being able to greet you with the proper courtesies. As you can see, I have a severe illness and can't perform intense movements. Just getting out of the house has already taken up most of my strength, and for that, I can only ask for your understanding."

Though Ubuyashiki Kagaya's voice was gentle, it was also forceful, making people involuntarily trust him.

Even Reiger, who usually had a calm demeanor, couldn't help but relax his expression slightly in the presence of Kagaya.

"There's no need for formality, Family Head Ubuyashiki," Reiger shook his head and said, "Though I was invited and have come here, I am but an ordinary guest, and my status is far beneath yours as the head of the Ubuyashiki family, so there is certainly no need for excessive courtesy on your part."

The Ubuyashiki family is an ancient clan with a history of over a thousand years, remaining prominent since the Heian period, bearing significant influence in the entire country.

This is evident from the fact that they could establish the Demon Slayer Corps without official support and have been running the Corps almost on their own.

Not to mention, in terms of financial strength, I remember as per the original story setting, even the lowest ranked "Kyu" level slayers receive a monthly salary of about two hundred thousand yen equivalent to the year 2019, and the Pillars can take as much salary as they want.

And all these salaries are distributed by the Ubuyashiki family, not to mention the expenses for the treatment of injured members, the follow-up work after battling demons, as well as costs during missions; all these expenditures are solely borne by the Ubuyashiki family.

This affirms that the Ubuyashiki family unquestionably possesses substantial financial resources; otherwise, they could not manage a Demon Slayer Corps independently for nearly a thousand years.

Understandably, being the Family Head and leader of the Demon Slayer Corps, Ubuyashiki Kagaya's position is extremely honorable.

In comparison, Reiger is merely a commoner and indeed does not warrant any grand gestures.

"Having said that, but you are neither a member of the Demon Slayer Corps nor obligated to slay demons, yet you have helped us defeat one of the Twelve Demon Moons' Upper Ranks. For this alone, we owe you a profound debt of gratitude,"

Ubuyashiki Kagaya softly said to Reiger.

"For over a hundred years, the ranks of the Upper Moons haven't changed, meaning that in all this time, no one has succeeded in defeating an Upper Moon. In contrast, our Demon Slayer Corps has seen countless Pillars perish at their hands."

As he spoke, Kagaya's voice filled with sorrow.

It was a lament for those who had sacrificed themselves.

The Pillars, too, bowed their heads, with a shade of gloom in their eyes.

The Twelve Demon Moons, being the highest-ranking and most powerful existence among demons, have always been the bane of the Demon Slayer Corps.

Most Pillars defeated Lower Moons; however, many Pillars also perished at the hands of the Upper Moons.

The Pillars of the Demon Slayer Corps and the Twelve Demon Moons are sworn nemeses of each other.

Any casualty among the Lower Moons was almost always at the hands of the Pillars.

And whenever the Pillars sustained casualties, it was almost always at the hands of the Upper Moons.

Both sides were such hunters and sworn enemies, with Pillars gaining fame by hunting Lower Moons and Upper Moons considering hunting Pillars their greatest achievement.

From Reiger's perspective, this was quite an ironic situation.

After experiencing the incident on the Infinite Train and subsequently defeating normal lower-ranked demons, as well as Lower and Upper Moons, Reiger had roughly confirmed the strengths of both the demons and the Demon Slayer Corps.

With the worst latent potential as the baseline, a demon who has just transformed and with dilute demonic blood and hasn't mastered Blood Demon Art was roughly equivalent to a Lv.1 adventurer, stronger than the average human, but ordinary humans are not entirely powerless against them.

A demon who has mastered Blood Demon Art, consumed humans, and gained some experience and strength is roughly equivalent to Lv.2.

Lower Moons are roughly equivalent to Lv.3.

Pillars of the Demon Slayer Corps and Upper Moons among the Twelve Demon Moons are roughly equivalent to Lv.4.

However, Upper Moons are generally stronger than the Pillars of the Demon Slayer Corps. To be specific, most Pillars are comparable to the lower tier of Lv.4, while the Upper Moons are at least at the upper tier of Lv.4. Additionally, demons inherently do not fear death, so whether it is severing limbs or piercing the body, as long as their heads are not chopped off by a Sun Wheel Blade, they can quickly recover as before. This gives them a naturally advantageous position when facing the Pillars of the Demon Slayer Corps.

Thus, within the Demon Slayer Corps, anyone who acquires the strength of a Pillar can swiftly exterminate Lower Moons, earn merits, and become a Pillar themselves. However, Pillars tend to fall short when facing Upper Moons and ultimately get defeated by them.

This has resulted in most Pillars throughout the history of the Corps dying at the hands of the Upper Moons, which explains why they harbor intense hatred towards the Upper Moons.

This is also why there was such a significant reaction from the Pillars upon learning that Reiger had slain an Upper Moon.

In the same vein, because the members of the Twelve Demon Moons are only ever killed by Pillars, the Upper Moons see the Pillars of the Demon Slayer Corps as enemies that must be eliminated, never sparing them when encountered.

Now that Reiger has slain an Upper Moon on behalf of the Demon Slayer Corps, causing a casualty among the Upper Moons that had not been seen in over a hundred years, this undoubtedly represents a milestone achievement for the Corps.

"Furthermore, with the appearance of the Sun Breathing technique in you, I can already feel it; in our generation, the Demon Slayer Corps and demons may finally determine a winner, ending this incorrect history that has lasted for over a thousand years."

Ubuyashiki Kagaya's voice became somewhat animated.

"Cough cough...!"

Due to the emotional upheaval, Ubuyashiki Kagaya suddenly began to cough violently.

"Lord!"

"My lord!"

"Please take care of yourself!"

The pillars were all greatly alarmed and hastily spoke out, while Ubuyashiki Kagaya's wife and daughter also quickly soothed his chest and back.

"Don't worry, I'm fine, I'm just too happy," he said.

After patting his wife and daughter's hands to reassure everyone, Ubuyashiki Kagaya turned to Reiger with a smile.

"You truly live up to the name 'Tsukiguni Yoriichi.' This may also be fate."

Upon hearing Ubuyashiki Kagaya's words, Reiger raised an eyebrow.

"Do you know Tsukiguni Yoriichi?" Reiger asked Ubuyashiki Kagaya.

"Of course," Ubuyashiki Kagaya replied, looking deeply at Reiger.

"Tsukiguni Yoriichi, a swordsman born in the Warring States period, was the first to master the breathing techniques and the first to create a breathing style."

"It was with his addition that the Demon Slaying Corps began to practice the breathing techniques under his guidance, acquiring the ability to confront demons in direct combat."

"However, the breathing technique that he himself created and used is said to be so powerful that it imposes strict physical demands on the user, and almost no one could learn it directly."

"As a result, various other breathing techniques have been derived from the one he used."

Ubuyashiki Kagaya turned his gaze to the pillars kneeling in the courtyard, his voice spreading slowly.

"Water Breathing, Thunder Breathing, Flame Breathing, Stone Breathing, Wind Breathing; these are the five fundamental breathing styles in the world of breathing techniques, derived from that of Tsukiguni Yoriichi."

"After the birth of these five basic breathing styles, the Demon Slaying Corps saw many geniuses who created other derivative breathing styles based on these fundamental techniques."

"Love Pillar Kanroji Mitsuri uses the Love Breathing, which is a derivative branch of Flame Breathing."

"Insect Pillar Kochou Shinobu uses Insect Breathing, and Serpent Pillar Iguro Obanai uses Serpent Breathing; both are derivative branches of Water Breathing."

"Sound Pillar Uzui Tengen uses Sound Breathing, which is a derivative branch of Thunder Breathing."

"Mist Pillar Tokitou Muichirou uses Mist Breathing, which is a derivative branch of Wind Breathing."

"In this way, various breathing styles have emerged in succession, but the breathing method of Tsukiguni Yoriichi's lineage, the origin of all, was lost."

As he spoke, a rich smile appeared on Ubuyashiki Kagaya's face.

"Until my generation, the original breathing, the ancestor and foundation of all breathing techniques, has finally reappeared in the world."

Upon hearing this, how could anyone not realize what Ubuyashiki Kagaya meant?

"Are you saying that this young man's Sun Breathing is the original breathing, the strongest breathing?" Shinazugawa Sanemi could not help but speak up.

The other pillars also looked at Reiger with astonished expressions, surprised by this sudden revelation.

"My lord!" Rengoku Kyoujurou even cried out, "How could such an important matter be unknown to us?"

Indeed, whether it be Sun Breathing or Tsukiguni Yoriichi, almost no one present knew of their existence.

This was quite unreasonable.

Sun Breathing is the ancestor and foundation of all breathing techniques, the strongest of them all, and Tsukiguni Yoriichi was the great swordsman who created this breathing technique and brought about the world of breathing styles. Why would such important information not be recorded and remembered within the Demon Slaying Corps?

"The reason is simple," Reiger answered the question.

"Tsukiguni Yoriichi once made a mistake and was expelled by the Demon Slaying Corps. Therefore, the legacy and records of Sun Breathing were maliciously obliterated by others, leaving almost no trace of them within the Corps."

The calm tone in which Reiger delivered this information caused a shock among all present.

"That's right," Ubuyashiki Kagaya sighed. "It's indeed a sad affair."