Isekai Adventure in the Dimensional Cube

The method to unlock the Supreme Domain, according to the original work's nature, is still quite unclear.

It is said that by pushing oneself to the limit and enduring pain, one can reach this Supreme Domain but before this, didn't anyone fulfill these conditions?

Certainly not.

The world is never short of people who strive with all their might and endure great pain, yet few among them have unlocked the Supreme Domain.

Therefore, awakening the Supreme Domain likely involves other conditions. Otherwise, Akaza wouldn't have pursued this realm for over a hundred years only to achieve nothing.

In the end, many of the pillars did manage to unlock the Mark and wield the Sun Wheel Blade, but those who could unlock the Supreme Domain were very few, only two or three individuals.

Thus, in Reiger's view, the Supreme Domain should be considered the most challenging ability to unlock among the three.

However, in the original work, there is a segment where Tanjirou's father refers to the Supreme Domain.

At that time, this is what Tanjirou's father said.

"The key is correct breathing and correct movements."

"With the minimal movement, exert the maximum strength, and gradually your mind will become clear."

"In the beginning, one must remember each movement and sensation closely, pick up these elements, open up all five senses, and recognize the full form of one's body down to every single blood vessel."

"At this stage, it feels extremely painful, as if continuing to struggle will only lead one into a dead end. After remembering and assimilating many things, eliminate the unnecessary parts and retain only what is essential for the movement, sealing off the rest."

"People tend to close their eyes when they really want to listen clearly, right? The same principle applies, select only what is essential in that moment."

"Over time, the opening and closing of blood vessels and muscles in the body will be as quick and simple as blinking, then light will appear and the path will open."

"Once the mind becomes clear, you can see the transparent world; it is the domain one reaches only after struggling and enduring pain to the utmost."

This was probably the most detailed information on how to unlock the Supreme Domain mentioned in the original story.

It is also because of recalling this past segment that, in the end, Tanjirou managed to successfully unlock the Supreme Domain.

Taking reference from these words and combining it with his own practical experience, Reiger finally reached a conclusion.

"I was able to unlock the Supreme Domain, probably because I gradually understood the correct breathing and movements while evolving the Sun Breathing technique and in order for the breathing technique and Magic Power to flow through the whole body, thus liberating my five senses to their full extent, realizing the entire form of my body down to each blood vessel."

"In that situation, the pain I felt back then might not have been merely due to attempting the Sun Breathing, but it might also have inadvertently touched upon a condition for unlocking the Supreme Domain."

"Then, over the course of three months as the breathing technique was progressively perfected, my body subconsciously memorized all the essentials and movements, eventually intuitively learning to concentrate by shutting down unnecessary senses, which cleared my mind and allowed me to see the transparent world."

This was why Reiger was able to directly unlock the Supreme Domain afterwards.

Drawing from this, Reiger summed up the method to unlock the Supreme Domain.

"Firstly, one must learn to concentrate, an unparalleled concentration that allows one's senses to fully expand and fully comprehend the proper shape of the human body, to the extent where every single blood vessel can be distinctly felt."

"Throughout this process, endure the torture that such intense focus brings to the brain's nerves until you can switch your senses freely and shut down the superfluous ones."

"Once the nerves withstand the intense concentration's pain and become resilient, the nerves undergo a transformation, and the mind also becomes clear."

That's when the Supreme Domain is attained.

"The trick lies in concentration!"

Reiger realized this.

This theory is also corroborated in the original work.

In the original, Himejima Gyoumei, Tokitou Muichirou, and Iguro Obanai—these three pillars were the ones who eventually unlocked the Supreme Domain.

At that time, they managed to unlock the Supreme Domain because they wanted to see through their opponent's movements, concentrating all their attention to discern the enemy's weaknesses.

Having an unmatched power of concentration, allowing one's senses to fully unfold and effortlessly control and govern them, opening and closing them at will—thus, the Supreme Domain would be unlocked.

"Concentrate!"

Reiger thus deliberately began training the pillars in this aspect.

But as mentioned before, there are no shortcuts this time.

Although unlocking the Mark could be facilitated by someone, and wielding the Sun Wheel Blade naturally follows after unlocking the Mark, only the Supreme Domain requires a solid, gradual understanding and meeting of conditions to be successfully unlocked.

Given this, even though Reiger consciously tried to lead the pillars in understanding, several days went by without anyone successfully unlocking the Supreme Domain.

Reiger kept engaging them in combat, guiding them during the battle and using combat to press them, teaching them to concentrate their minds during the fight.

Days like these continued for a whole week.

And that week was full of discussions for the entire village of the Swordsmiths.

...

"Boom!"

Near the Swordsmiths' village, a burst of flames unexpectedly shot into the sky, causing a thunderous boom that shook the entire village.

Almost everyone in the village heard this massive boom.

However, instead of being startled, they began discussing it animatedly.

"It has started again, the Grand Master and the pillars' special training."

"Every time it causes such a big commotion, it truly befits the strongest Swordsmen of the Demon Slayer Corps,"

"I heard it seems to be the Grandmaster training the current Pillars, so that's why it stirs such a big commotion."

"I see, that's not surprising then."

The swordsmiths in the village were all more composed than one another.

At first, they were very panicked too.

Sudden loud noises, sudden explosions, had made the people of the swordsmith village think that the Demon Slayers had come, almost causing a panic.

But after a week of continuous explosions and thunderous noises like these, they had grown accustomed to it.

Especially after learning that the initiator was the Demon Slayer Corps' new Grandmaster, the swordsmiths were all enlightened.

"So it's the owner of the Divine Blade demonstrating his power, then there's nothing to worry about."

Indeed, now Reiger in the eyes of the swordsmiths of the village, was almost no different from being omnipotent.

The appearance of the Divine Blade led these swordsmiths to regard Reiger as a god-like figure worth their worship, thus forming such a subconscious belief that if it was him, no matter how exaggerated the actions, it was quite normal.

Moreover, those who had seen the sage knew that the Divine Blade emitted high temperatures, and in the hands of its owner, a casual wave could cause a large fire, as if the Fire God had descended."

With this belief, all the swordsmiths assumed that the repeated flames and explosions were caused by the owner of the Divine Blade wielding it, and thus their attitude toward the Divine Blade became increasingly fanatical, and their respect for Reiger grew.

Of course, the people of the Demon Slayer Corps did not see it this way.

"What? The Grandmaster is training the Pillars?"

"Do the Pillars need someone to train them too?"

"These flames and loud noises are caused by the Grandmaster? Really?"

"Incredible!"

This was the reaction of the members of the Demon Slayer Corps.

They had been in the Demon Slayer Corps for quite some time, and Reiger had only appeared less than a few months ago, how would they know how strong Reiger was?

Even if people repeatedly claimed that the Grandmaster had killed several Upper-Rank demons with a single slash during an attack at headquarters, for many, it was just a matter worth marveling at, not having witnessed it firsthand, they could not fully grasp the impact.

On the other hand, many people in the Demon Slayer Corps had seen the Pillars in action, including many members of the elite who had seen the Pillars fight.

In their eyes, the Pillars were undoubtedly very strong, so powerful they seemed ghostly divine — even for a demon as strong as those of Lower Ranks of the Twelve Demon Moons, they were no match for the Pillars.

Thanks to this, no matter whether it was members of the Demon Slayer Corps or the elite, all revered the Pillars, and many even could not help but kneel and bow in their presence, showing a picture of utmost fear and respect.

And now they were being told that these powerful, fearsome Pillars were taken for special training by the current Grandmaster?

One could not help but question the truth of this matter!

However, such doubts would completely disappear in a few days.

The reason was simple.

After nearly a month, the training grounds near the swordsmith village were finally completed and opened to ordinary members for training.

Then, on the first day that the training ground officially opened to the public, all the members of the Demon Slayer Corps witnessed a scene that was extremely shocking.

"Boom!"

In the midst of a loud boom, one powerful Pillar after another was blasted away by the explosions, falling to the ground, miserably rolling a great distance away.

And at the center of the explosion, Reiger, holding a Sun Wheel Blade flickering with red light and emanating high temperatures, chastised the Pillars lying on the ground.

"How many times have I said not to just use your eyes and instincts to watch my movements, but to open up all your senses, first observe yourself, then observe me!"

"Discard unnecessary movements, discard unnecessary perceptions, focus your mind!"

"Focus!"

"Again!"

Under Reiger's scolding, the Pillars shakily got up from the ground, covered in dirt and soot, looking extremely disheveled.

Even Kochou Shinobu and Kanroji Mitsuri, regarded as goddesses, looked like two little dirt dogs, completely covered in dust.

"Aaaaaaaah!"

The Pillars then collectively screamed and charged towards Reiger again.

"Boom!"

After another loud noise and a sweeping blaze, the Pillars were once again thrown out like trash, tumbling to the ground.

Witnessing this scene, the people of the Demon Slayer Corps were stunned.

Before long, when they looked at Reiger, their eyes were filled with fear.

"He completely overpowered all nine Pillars...?"

From that day on, no one questioned Reiger's strength again.