Isekai Adventure in the Dimensional Cube

Abnormalities around Reiger swiftly captured the attention of everyone present.

"Has the sensation of the fighting spirit changed?"

Akaza's eyes narrowed slightly.

In his perception, the fighting spirit emanating from Reiger had suddenly changed.

The change wasn't drastic, it was still massive, still unconventional, but it carried the sensation of a dangerous substance flowing within, at least to him (the demon).

Unlike Akaza, each of the others at the scene detected the anomaly in their own way, and each felt differently about it.

"His, his heartbeat suddenly got so fast!"

Zenitsu, who had been squatting with his head in his hands, blurted out nervously.

"I have this tingling sensation all over my skin, what is the lunchbox guy doing?"

Inosuke rubbed his arms that were exposed to the air.

"The rhythm and precision of the breathing have changed."

Rengoku Kyoujurou was somewhat surprised, somewhat puzzled.

As for Tanjirou, he stared blankly at Reiger at this very moment, and for some reason, he felt like he was seeing something very familiar.

The atmosphere emanating from Reiger at this moment gave Tanjirou the uncanny feeling of seeing his father, who had already passed away.

In a trance, Tanjirou even thought he saw a snowy field, and his father, dressed in priestly attire, performing the Shen Yue Dance within it.

Then, the vision abruptly changed to a scene he had recently experienced.

In a mountain infested with spiders, a demon stood in silence.

There were characters inscribed in the demon's eyes.

Unlike Akaza, who had characters in both eyes, this demon had only two characters inscribed in the left eye.

The character on top —— "Lower."

The character below —— "Five."

Indeed, it was Rui, Lower Rank Five of the Twelve Kizuki, who had been exterminated not long ago.

A few months earlier, Tanjirou had encountered this demon from the Twelve Kizuki and they had clashed.

In that clash, he was beaten brutally, hurt by irrational violence repeatedly, knocked down time and again, and even his sword was broken, rendered like a butterfly caught in a spider's web, becoming the demon's prey.

The demon had fired threads capable of grinding human flesh into mince, weaving those threads into a web, quite literally trapping him with no escape.

Yet, in the very end, he managed to execute "that" technique.

"The God of Fire's Shen Yue· Waltz."

It was the Shen Yue Dance his father used to perform in the snowy field.

It was the "Form" that his father had taught and used.

It was when facing the monstrously unbeatable spider demon and pushed into a corner that Tanjirou performed the Shen Yue Dance's form that had been passed down through his family for generations, even using an unknown breathing technique, unleashing incredible power and momentarily overcoming Lower Rank Five.

This time, Tanjirou had come to the Infinite Train to find Rengoku Kyoujurou not only because of the Demon Slayer Corps' mission but also to seek Rengoku Kyoujurou's insight on why the God of Fire's Shen Yue could transform into a combat-ready breathing technique.

This was suggested by the current Insect Pillar, Kochou Shinobu.

As one of the few pillars who harbored goodwill towards Tanjirou, upon learning about the God of Fire's Shen Yue from him, she believed that Rengoku Kyoujurou, who was proficient in Flame Breathing, might know something.

This was because the God of Fire's Shen Yue and Flame Breathing were akin in power; both unleashed sword techniques that conjured fierce flames.

Therefore, Tanjirou came here, to Rengoku Kyoujurou's side, to unravel the secrets of the God of Fire's Shen Yue, which had been a heritage of his family for generations.

Unfortunately, before Tanjirou had the chance to find an opportunity to ask, the incident on the Infinite Train occurred.

And now, Tanjirou was astonished to discover that Reiger, who was confronting Akaza and holding Rengoku Kyoujurou's Sun Wheel Blade, entered into a state of Total Concentration·Breathing, the sensation was identical to when he and his father used the God of Fire's Shen Yue.

What was happening?

Tanjirou could not utter these words.

Because, he smelled the scent of danger.

"Be careful!"

Realizing that the scent was coming from Akaza's direction, Tanjirou couldn't help but shout out loud to Reiger.

But just as his voice rose, Akaza's brewing death blow was already unleashed.

"Destructive Kill· Annihilation Style!"

A terrifying force burst out around Akaza, transforming into a dreadful shockwave that, akin to an explosion, followed his thrusting fist, barreling towards Reiger.

This was the most powerful among the six martial arts moves named "Destructive Kill" by Akaza, concentrating all fighting spirit and strength into one punch, giving this punch a destructive force that could obliterate everything.

After sensing an ever-increasing threat from Reiger's fighting spirit, Akaza held back no longer and used this move straight away.

Such a strike, if directed against the Infinite Train as Reiger had done before on the tracks, might not have disassembled the train completely, but a head-on collision with the locomotive would certainly shatter it.

This immensely powerful blow, like a tsunami, caused the shockwave to sweep out explosively, tearing through the earth and the atmosphere, roaring towards Reiger with overwhelming momentum.

"————!?"

Rengoku Kyoujurou and the others' faces changed dramatically as they all shouted something in unison, but their voices were drowned out by the explosion-like blast, and they were blown away by the shockwave, vanishing from their original spot.

Reiger, holding the Sun Wheel Blade, faced this attack and appeared as powerless and fragile as a human about to be engulfed by a tsunami.

But facing this devastating strike, Reiger inexplicably closed his eyes.

"Boom!!!"

The explosion-like shockwave instantly engulfed Reiger's figure, shattering the ground where he stood to pieces.

However, in the midst of that formidable shockwave, flames appeared.

Like the sun rising at dawn.

Like light appearing in the darkness.

Flames blazed up, and then suddenly expanded.

"Boom!"

In the roar, the shockwave was split in two by the sudden surge of flames.

Thus, a fierce wind howled, dust filled the sky, and the severed shockwave was swept in all directions, raising relentless gales that whistled ferociously.

The flames that had cleaved the shockwave leapt up, turning into a dazzling wheel of fire, burning through the atmosphere, pushing back the shock, and like a fleeting ray of sunlight, it suddenly sliced through the void, arriving in front of Akaza!

This breathtaking strike, as if a sprite of the sun had appeared in the world to dance gracefully, left Akaza only time to shrink his pupils to the size of pinpoints, unable to do anything else, not even to change his stance, still maintaining the posture from which he had launched the "Destructive Kill· Annihilation Style."

In that instant, the flying flames sliced across Akaza's field of vision, through his fighting spirit, and finally directly across Akaza's neck, disappearing behind him.

"Sun Breathing Technique, First Form."

Reiger then appeared where the flames had vanished, standing behind Akaza, his back to him, slowly sheathing his sword.

"Round Dance."

Everything, in that moment, returned to calm.

The shockwave was gone.

The flames were gone.

The destructive power was gone.

The sunshine, too, was gone.

As if none of it had ever existed, as if all that had just happened was just an illusion, the whole place became deathly quiet.

"————"

Whether it was Rengoku Kyoujurou, or the trio of main characters, they all lay on the ground, eyes wide open, watching this unfold, completely voiceless.

Akaza fell silent as well.

Reiger, too, remained wordless, standing with his sword sheathed, his expression unchanged, utterly serene.

This silence lasted for who knows how long.

"What is your name?"

At a certain moment, Akaza asked with a hoarse voice, seeking an answer to this question that he had not gotten before.

Reiger didn't turn around.

However, he did hear Akaza's voice.

But upon hearing Akaza's voice, Reiger's first reaction was not to give his name but to recall that dream, to recall the swordsman who had passed on every move of "Sun Breathing Technique" to him, without missing a single detail.

"Ting-a-ling——"

Off to the side, Tanjirou, still in a daze, had the paper flower earring on his ear sway perfectly, making a sound like a wind chime.

"Tsukiguni Yoriichi."

Almost as if possessed, Reiger gave that name.

"Tsukiguni Yoriichi..."

Akaza's voice began to slow down, to grow quieter.

"I will remember this name."

As soon as these words were spoken, Akaza's head began to slowly shift out of place from his neck and fell from his body.

With a "thump," the body of Akaza, now without a head, also collapsed, bereft of any trace of life.

Upper Moon Three, Akaza, was defeated here.

Facing this enemy that could alarm even the Pillars, a youth who had not even joined the Demon Slayer Corps, who was not a Ghost Hunter, and who didn't even have a Sun Wheel Blade, had used only one strike.

One strike to slay the Upper Moon.

This was a stunning achievement.

This was a terrifying accomplishment.

Rengoku Kyoujurou and the others simply stared blankly at this scene, unable to regain their composure for a long time.

"...Round Dance?"

Only Tanjirou, stupefied, watched Reiger sheathe his sword, then thought back to the sword technique just now, which resembled the sun wheel, his mind in complete disarray.

His senses were not mistaken.

The sword technique Reiger had just used was indeed very familiar to him.

Whether it was the Dance of the Fire God that he had used against Lower Moon Five on Spider Mountain a few months ago, or the technique Reiger had just used against Upper Moon Three, its name was—"Round Dance."

"Sun Breathing Technique?"

Tanjirou's mind was in complete chaos, utterly unable to think for himself.

Unaware of all this, Reiger had already left the battlefield and approached Rengoku Kyoujurou.

"Your sword isn't bad," Reiger said with a slight smile. "It's just too heavy."

At those words, Rengoku Kyoujurou started to smile wryly.

The incident on the Infinite Train had finally come to a true end here.

About ten minutes later, a group of swordsmen in Demon Slayer Corps uniforms arrived swiftly from the other side of the tracks with a group of masked people, starting to clean up the scene, to tidy up the aftermath.