Ultimate Being from the Tokonosu City

Unlike the original protagonist, who didn't go to school, so he could hardly express his thoughts on how he could awaken the Demon Slayer Mark, Isao's explanation was precise, logical, and easy to understand. However, this was also why they were at a loss when they heard the requirement to unlock the Demon Slayer Mark. 

The talent and hard work were one thing, but its following requirement was crazy. 

"Do you mean we have to endure and survive under a heart rate of over 200 beats per minute and a body temperature of over 39 degrees Celsius?" 

"Yes." 

"You are going to die!" 

"That's why I told you that only those who were talented could open the Demon Slayer Mark." 

His words were understood by everyone, and they knew how difficult it was to open the Demon Slayer Mark, especially when one had to survive such a life-threatening situation.

In other words, those who could do it were only among the Hashira and those who might have a chance to become a Hashira, but to keep everyone's safety, it was necessary to keep this matter a secret between them, or else, one mistake would lead to the majority of the members to die as they were unable to bear such situations. 

"Naturally, if you can open it, there are many benefits that you can get." 

"Such as?" 

Hearing those words, everyone became curious. 

Isao didn't hide anything and listed, one by one, all the abilities that one could gain from awakening the Demon Slayer Mark. 

The first one was an enhanced physical ability, which made them become even much stronger. 

Yes, using a breathing technique made one stronger, but when one was able to open the Demon Slayer Mark, one could become even more powerful. 

This was the first, and there was also the second, which was—

"Transparent World?"

"Yes, it is an ability that allows you to perceive the bodies of others as if their skin were transparent. It will help you track the flow of blood, breathing, muscular contractions, and joint movements of the person you are looking at, which can be used to predict their movements and evade their attacks with ease. 

"Moreover, those who can access the Transparent World can perceive the world in slow-motion, further increasing their reaction and movement speed." 

"..." 

When two of the benefits were mentioned, everyone was naturally eager to open the Demon Slayer Mark. Their weakness was something they hated the most. If they were more powerful, then wouldn't they be able to defeat Muzan and those demons, erasing them from this world and protecting those whom they cared about? 

Moreover, there was no need for them to rely on Isao, but at the same time, if it wasn't because of him, would they even know the Demon Slayer Mark existed?

Yet, at the same time, there was one question that had been bothering them. 

"I see." Kagaya nodded. "This is a wonderful power." He hoped that everyone could also awaken the Demon Slayer Mark, but he was also confused. "But why shouldn't we tell Kanae-san this power?" 

Yes, this confused them, and they wondered why Isao told them to promise not to tell Kanae this. 

Why? 

They didn't think that Isao was stingy, especially when he had told them everything, so there must be some sort of reason why he told them not to say anything to Kanae. 

"To gain something, you will lose something." 

Isao admitted that the breathing style was powerful, but this technique was dangerous. "Since you have gained so much power, something must be taken from you. In this case, it is your vitality." 

"Vitality?" 

"What do you mean?" 

They were confused by his words. 

"In other words, when you open the Demon Slayer Mark, your lifespan will be reduced in exchange for greater powers." 

"....." 

All of them fell into silence, and they wanted to ask whether Isao was lying or not, but why should he lie? 

So, at this moment, no one could say anything and just contemplate the meaning behind his words. 

At the same time, since Isao had awoken the Demon Slayer Mark, then should his lifespan be reduced, too? 

When Shinobu, Amane, Hinatsuru, Makio, and Suma understood this, their expressions became pale. 

In exchange for power, your lifespan would disappear. 

This was fair, right? 

Yet, how could they accept Isao's death?

"...reduced lifespan?" 

After a moment of a daze, Kagaya asked. 

"Yes." Isao nodded. "I can't say for sure how much your lifespan will be reduced, but according to my observations with my own body, well... I can't for sure, but at least you will be able to stay alive until you are 25 years old." 

Unlike him, who had devoured the DNA of the demon within him, which gave him almost unlimited vitality, the others couldn't do it as they were just a normal human, and he didn't think that they wished to become a demon either due to how hatred they had toward such an existence. 

While Isao had to admit that this organization was kind of dubious and might even force many poor young people to fight a dangerous creature, their goal to erase the demon from this world was real, and this was one thing that Isao had never doubted since, in the end, the ploy, and many other things were used to him by Kagaya so he could fight against those demons. 

However, Isao had to say he didn't like Kagaya. 

"...." Everyone. 

Yet, everyone was at a loss when they heard his answer. 

'25 years old...' 

What was the age of Isao again? 

They couldn't ask, nor did they dare to ask this question. 

It was also impossible for Isao to tell them about his ability since he didn't even tell his women, so why should he tell them?

Still, this also made them understand why Isao told them that his time was limited. 

Isao had awoken the Demon Slayer Mark, and he could only live until he was 25 years old. 

They also understood why Isao asked them to promise him not to tell Kanae.

At that moment, their feelings were completely complex, and they didn't know how to face him. What kind of expression should they look at him now? Yet, for one thing, it was impossible for them to see him the way they saw him before. 

Isao understood he didn't have a long life, and when he reached 25 years old, he would die. 

Knowing when you die, could they imagine it? 

They could say whatever they wanted, saying that he was greedy, evil capitalist, or whatever, but they had a long life, but he? 

"Oh, by the way, if you are over 25 years old, then it is still possible for you to open the Demon Slayer Mark, but you will die at least in a few hours." 

"..." Everyone. 

Now, after hearing all of that, what should they say? 

Even Kagaya, who understood the work of a human heart, was also at a loss. 

Looking at all of their expressions, Isao knew that they had misunderstood him, and they thought that he would die at 25 years, but it didn't matter since it worked in his favor. Moreover, before he reached 25, he could imagine the Demon Slayer Corps would dissolve due to the eradication of demons, so even if they knew that he didn't die.

How could he be so sure? 

Because Isao was going to end Muzan and the rest this year. 

There was no need to waste his time, and he was going to erase all of the demons in this world so he could enjoy his life there. 

At the same time, he saw that the system gave him two new worlds to which he could travel anytime. In total, there were five worlds that he could visit: three unknown, this world, and the world of "High School of the Dead." 

While he was curious, he decided to endure it and waited until he finished all the demons. 

"That's all I know about the Demon Slayer Mark." Isao then looked at Kagaya and asked, "Are you satisfied?" 

"Ah, yes, thank you, and I am sorry." Kagaya bowed his head deeply. 

Isao didn't care about Kagawa's apology. Instead, he looked at all the Hashira, who could not meet his eyes, and then asked, "So, who is going to teach me their breathing style first? Let's not waste time." 

"....." 

Hearing his words, they were at a loss, but then Rengoku quickly raised his hand. "I-I will do it." 

"Good, let's go to the yard." 

"Okay." 

Watching how Isao treated this place as his house, no one said anything, which made Isao admit that all the people in the Demon Slayer Corps were good people. 

Yes, they might be shitty sometimes, but they were all good people. 

'Fortunately, I am a good guy.' 

If Isao was a bad guy, then this group of good people would be deceived by him to death. 

That said, it was his time to work hard and think about what kind of weapon he should ask to craft. 

---

I have added five more advanced chapters!

It is tough, but I work hard!

Anyway, there are 35 advanced chapters now. By the way, he will return to the world of "High School of the Dead," and when it is over, he will go to the world of "Danmachi."

Sorry for those who expect Baki, but frankly, I was thinking of going after Kozue's mother, the neat and beautiful widow, but somehow, I decided not to do it because I felt like it might be boring.

Nevertheless, please enjoy~!