Isekai Adventure in the Dimensional Cube

In his lifetime, Tsukiguni Yoriichi had only one encounter with Kibutsuji Muzan.

At that time, the Demon Slayer Squad had just recently introduced the breathing techniques pioneered by Tsukiguni Yoriichi, which had indeed narrowed the power gap between humans and demons. Yet Kibutsuji Muzan still believed that the mere human Demon Slayer Squad posed no threat to a powerful demon with extraordinary abilities. Thus, he did not actively seek to eliminate the squad.

Especially after clandestinely observing the performance of the most outstanding swordsmen of the Demon Slayer Squad, Kibutsuji Muzan was even more convinced that he, as a perfect creature, could not be defeated. Although he was initially interested in the breathing techniques, his interest quickly faded.

That was until the day Kibutsuji Muzan encountered Tsukiguni Yoriichi.

In that encounter, Kibutsuji Muzan made only one move, but as a result, he was severely wounded by Tsukiguni Yoriichi in an instant, so badly injured that he was unable to recover and regenerate his body, nearly dying on the spot.

In the end, Kibutsuji Muzan fled, splitting his body into over eighteen hundred pieces to distance himself from Tsukiguni Yoriichi and went into hiding until Yoriichi's death, daring not to show himself again.

Because of that encounter, for the first time since becoming a demon, Kibutsuji Muzan felt the fear of death, and he was deeply afraid of the man who seemed to have been born to defeat him, leaving behind a lifelong psychological shadow.

After that, Kibutsuji Muzan no longer ignored the Demon Slayer Squad. To thoroughly eradicate them, he created the Twelve Demon Moons and even personally attacked the Demon Slayer Squad after Yoriichi's death, completely eliminating all swordsmen who knew the Sun Breathing technique, severing its lineage.

Since then, the Demon Slayer Squad and the Ubuyashiki Family leading them became the thorn in Kibutsuji Muzan's side, the main targets of the Twelve Demon Moons. They were driven to the brink of destruction by demons numerous times over hundreds of years, nearly facing catastrophic ruin.

This is why the Demon Slayer Squad turned to the shadows, ceased cooperation with officialdom, and began to hide the headquarters and the tracks of the Ubuyashiki Family.

All of this was because of that man—Tsukiguni Yoriichi.

He was the first human to cast a shadow of death over Kibutsuji Muzan, the only one in a thousand years who came close to killing him.

Tamayo was fortunate enough to have witnessed the scene where Tsukiguni Yoriichi nearly killed Kibutsuji Muzan.

Because of her expertise in pharmacology, Tamayo was turned into a demon by Kibutsuji Muzan and kept by his side, in the hopes of using her knowledge to create a medicine that could overcome sunlight.

Thus, Tamayo witnessed it all.

"I really want to kill Kibutsuji Muzan, even in my dreams,"

For the first time, hatred appeared on Tamayo's beautiful and dignified face.

"But I am very aware of how powerful and terrifying he is. For a thousand years, only Tsukiguni Yoriichi had a chance and the ability to kill Kibutsuji Muzan, but in the end, he let him escape, just by a little bit."

Saying this, Tamayo was truly helpless and angry.

It was unavoidable.

According to Reiger's knowledge of the original story, Tamayo became a demon solely because she was deceived by Kibutsuji Muzan. For this, she even killed her own husband and child, and fell into an endless cycle of guilt and pain.

The depth of this guilt and pain was indicative of how much hatred she had for Kibutsuji Muzan.

So, what Tamayo said was right; she did indeed want to kill Kibutsuji Muzan. She regretted that Tsukiguni Yoriichi had not managed to kill him to the extent that she almost bit through her lips.

"After Kibutsuji Muzan escaped, because of the heavy damage, his control over me weakened, and I was able to break free from his control and gain my freedom. I was also spared by Tsukiguni Yoriichi and entrusted with the task of assisting humanity in defeating Kibutsuji Muzan, the demon he couldn't defeat."

Tamayo raised her head, looking at Reiger.

"Under these circumstances, can you understand how I felt when I heard the name 'Tsukiguni Yoriichi' from Tanjirou?"

Need that even be said?

She was undoubtedly profoundly shocked!

Restless, Tamayo even used this word herself, which sufficiently illustrates how shocked and conflicted Tamayo felt in her heart, knowing that there was a swordsman called Tsukiguni Yoriichi who suddenly appeared and easily killed the Upper Moon Three.

Therefore, she decided to come here, to seek out Reiger.

"Before coming here, I couldn't help but hope that Tsukiguni Yoriichi was indeed still alive, even though I knew it was unrealistic," Tamayo said with a bittersweet smile to Reiger, "but after seeing you, sir, I felt that maybe I could still continue to hope."

"Oh?" Reiger responded calmly, "Why do you say that?"

"Because you are very strong," Tamayo said insistently, looking straight at Reiger, "When I first saw you, I almost thought I was really seeing Tsukiguni Yoriichi."

Since mastering the ability to perceive the world, Reiger had been able to conceal his fighting spirit and presence effortlessly.

This meant that when others laid eyes on Reiger, he was just an ordinary swordsman with hardly any presence.

But therein lay the problem.

Could a swordsman capable of easily killing the Upper Moon Three be someone who seemed to have no presence, just an ordinary person?

Of course not!

And yet, Tamayo had seen such a person once before, hundreds of years ago.

Yes, it was Tsukiguni Yoriichi.

When Tamayo first met Tsukiguni Yoriichi, he gave her the same impression as Reiger did at this moment: no presence, ordinary, lacking any hint of fierceness.

Yet it was this unremarkable, ordinary swordsman who had inflicted such severe injuries on Kibutsuji Muzan in a blink of an eye.

Since then, the figure of Tsukiguni Yoriichi had left an exceedingly deep impression in Tamayo's heart.

The figure of Reiger in this moment completely overlapped with that of Tsukiguni Yoriichi from Tamayo's memories.

Just this alone made Tamayo unable to help but harbor hope.

"You might be able to fulfill Tsukiguni Yoriichi's will and slay Kibutsuji Muzan in this era,"

Tamayo said to Reiger.

From Tamayo's words, Reiger could hear the longing as well as a strong hatred and dedication.

This dedication, Reiger had seen it in someone else as well.

Ubuyashiki Kagaya, the current Family Head of the Demon Slayer Corps, had the same underlying intense dedication when he spoke in front of Reiger about ending the millennium long misguided history of demons against humankind.

Kibutsuji Muzan, the demon king born in the Heian era, had created far too many tragedies.

All demons were born from his hands; thus, for every demon that came into existence, a tragedy occurred.

And the tragedies caused by those demons as they killed and devoured humans could all ultimately be traced back to Kibutsuji Muzan.

To completely eradicate demons, to utterly remove the man-eating monsters, to ensure the night was no longer dominated by demons, and to prevent humans from dying at the hands of their cruelty, it was necessary to kill Kibutsuji Muzan.

As long as Kibutsuji Muzan, the demon king, died, then all demons in this world would disappear.

All demons had transformed from humans into demons because of Kibutsuji Muzan's blood.

Including the demon in the wooden box that Tanjirou always carried around – it too was created because Kibutsuji Muzan forcibly injected his blood into it.

Whether it was Tamayo, Ubuyashiki Kagaya, or even including all the Ghost Hunters, all the Pillars, and everyone who lost their families and suffered from the pain caused by demons, they all hoped for the death of Kibutsuji Muzan.

Kibutsuji Muzan was the one person that the Demon Slayer Corps wanted to eradicate at all costs, and no one within the Corps would hesitate to gamble the lives of everyone to achieve this.

"Since you're also called Yoriichi, then in any case, you must have some profound connection to that person, right?"

Tamayo asked quietly.

In response, Reiger remained silent for a while before finally speaking.

"I only received a gift from him, along with a message,"

Reiger said calmly.

"What?"

Tamayo was stunned.

"'I leave it in your hands.'"

Reiger looked directly at Tamayo and said, "That is what he told me."

Upon hearing that, Tamayo remained in shocked silence for a long time.

"Miss Tamayo."

Seeing this, Yushirou, out of concern, called out to Tamayo and inexplicably shot Reiger a glare.

"I'm fine."

Tamayo shook her head, lowered it, and it seemed as if she wiped the corner of her eye.

Then, Tamayo suddenly said,

"This time I came not only to meet you and confirm some things but also to tell you two pieces of information," Tamayo said to Reiger. "Akaza, that Upper Moon Three, may not be dead."

"What?"

This time, it was Reiger who was taken aback.

Akaza was not dead?

"It's true," Tamayo told Reiger with a serious face. "To be frank, I've always been looking for an opportunity to study Kibutsuji Muzan's blood to create a medicine that could turn demons back into humans, so I have been closely monitoring those demons who have a substantial amount of Kibutsuji Muzan's blood, intending to collect it."

Reiger knew about this.

Tanjirou had taken on this task from Tamayo, promising to help collect the blood of demons for her.

And their first target was, naturally, the strongest of the Twelve Demon Moons.

"I have been closely following the Upper Moon Three, Akaza. During the Infinite Train incident, Tanjirou attempted to collect his blood but couldn't find his body."

"Tanjirou thought he was too late to prevent Akaza's body from disappearing, considering that demons decapitated by the Sun Wheel Blade turn directly into ash,"

"But based on the timing Tanjirou provided, the body of an Upper Moon like Three wouldn't fade to ash so easily,"

Tamayo explained to Reiger her reasoning for believing Akaza might not be dead.

Thanks to her words, Reiger remembered.

Not all demons who were decapitated by the Sun Wheel Blade died accordingly.

But just as Reiger remembered this, suddenly, a loud noise erupted.