In a week's time, even though the training ground for the Demon Slayer Corps had not yet been developed enough for many members to use simultaneously, it was sufficient for a dozen or so people to train together without a problem.
Consequently, Riezel brought a group of Hashira to this place, an open space surrounded by countless trees, with piles of lumber in the corners from recent logging.
"Is it really here?" Tengen looked at the still-undeveloped land with some disdain. "This place isn't flashy at all."
"Uh... I think making it flashy wouldn't help much anyway..." Mitsuri said, sweating a little.
"This should have been developed by the villagers and the Kakushi, right?" Kyoujurou looked around and said loudly. "Umu! Not bad! They worked hard!"
"It won't be long before this place can be officially used..." Shinobu explained to everyone. "At that time, all the members will be able to train here."
"It doesn't matter what they do." Sanemi said coldly. "No matter what, the quality of the Demon Slayers has been declining lately. How much strength can they really gain from training now?"
"I agree." Obanai chimed in, playing with the white snake around his neck. "Instead of letting weak members participate in the upcoming battle and lose their lives for nothing, it's better to exclude them from the start."
"It won't do." Gyoumei stated calmly, hands clasped together and tears flowing. "They joined the Corps because they wanted to eliminate demons, either because they lost their loved ones to demons or had them eaten by demons. If we exclude them in the upcoming battle that will decide everything, it will surely lead to much resistance, even conflict. If this causes chaos in the Corps before we even start fighting, it will bring more harm than good."
Only Giyuu and Muichirou stood silently on the side, one silent and the other dazed, not participating in the argument at all.
Riezel naturally had no interest in discussing the internal affairs of the Demon Slayer Corps with the Hashira.
"You can discuss these matters properly after you go back." Riezel interrupted their argument. "Instead of worrying about those ordinary members, you should worry about yourselves first."
"Whether you can awaken the Mark, the Bright Red Nichirin Sword, or the Transparent World is still unknown. Do you really have the leisure to worry about others?"
Upon hearing this, all the arguing Hashira fell silent.
"What should we do?"
Rarely speaking, Giyuu steered the topic back on track.
"Don't rush." Riezel said calmly. "We need to consider which ability you should try to awaken first."
As soon as he finished speaking, several Hashira immediately expressed their opinions.
"Is there even a question?" Sanemi said with a terrifying smile. "Of course, it's the Mark!"
"That's right..." Obanai said in a low voice. "Awakening the Mark, which can directly increase our strength, is the most important for us."
Riezel didn't think much of the Demon Slayer Mark, but for the Hashira, it was the most valued of the three abilities.
While the Bright Red Nichirin Sword could enhance killing power against demons, it couldn't directly increase their strength. Relying solely on this ability against the Upper Ranks wouldn't necessarily give them an advantage.
Of course, the Transparent World was similar.
While it could enhance their senses and perception, it wasn't as straightforward as the Demon Slayer Mark, which directly increased strength.
For this reason, the Demon Slayer Mark was undoubtedly the ability the Hashira valued and desired the most. If, by the time the decisive battle arrived, they couldn't awaken all three abilities and only had time to gain one, they hoped it would be the Demon Slayer Mark.
As for its terrifying side effect, in the determined minds of the Hashira, it was as if they didn't exist.
"The Mark, huh?" Riezel glanced deeply at the gathered Hashira, then continued, "Though I'd like to commend your reasoning, the awakening difficulty for the Mark isn't low."
"Just spill it! Young Tsugi—I mean, Head Instructor Tsugikuni!"
Kyoujurou, fearless as ever, shouted at Riezel.
"What do we need to do to awaken it?"
"It's simple." Riezel didn't hold back, answering frankly. "To awaken the Mark, you just need to reach a body temperature of 39 degrees Celsius and a heart rate of over 200 beats per minute."
Upon hearing his answer, all the Hashira froze.
"Body temperature of 39 degrees?"
"Heart rate over 200 beats per minute?"
"...That's it?"
They couldn't help but utter such words.
Not for any other reason but because it sounded too simple.
Indeed, raising one's body temperature to 39 degrees and heart rate above 200 beats per minute posed a significant challenge for the body to endure.
Still, the Hashira had thought that awakening the Demon Slayer Mark required a very special method, something so unique it would be difficult to achieve. Otherwise, how could it be that after so many years, not a single Demon Slayer capable of using the Demon Slayer Mark had appeared in the Demon Slayer Corps?
Yet right now, their head instructor was telling them that simply raising their body temperature to 39 degrees and heart rate to over 200 beats per minute would awaken the Demon Slayer Mark.
This truth truly puzzled the Hashira.
"I know what you're thinking."
Riezel saw the confusion in their eyes and explained.
"These conditions might not be easy for an average person to meet, but for you, raising your body temperature to 39 degrees and heart rate to over 200 beats per minute during battle isn't that difficult. Nonetheless, this is indeed the condition for awakening the Mark."
What he said was indeed the truth, as the original work made this point very clear—the conditions for awakening the Demon Slayer Mark were exactly that.
However, the problem was—
'Why hasn't a single person in the Demon Slayer Corps awakened the Mark with such a simple condition?'
Riezel was also quite puzzled about this.
From his current perspective, raising one's body temperature to 39 degrees Celsius and heart rate to over 200 beats per minute during battle was something any Hashira could easily achieve.
The evidence lay at the end of the original work, where almost all the Hashira successfully awakened the Demon Slayer Mark in battle after learning its awakening conditions.
Riezel also didn't believe that in all the past battles, there wasn't someone who happened to raise their body temperature to 39 degrees and heart rate to over 200 beats per minute during intense combat.
Yet the fact was, since the first generation of Demon Slayers had successively died due to the side effect of the Demon Slayer Mark, hardly anyone in the Demon Slayer Corps had successfully awakened it again.
'Why is that?'
After pondering carefully, Riezel thought of a reason.
"It seems like the Mark has a particular characteristic..." Riezel continued his explanation. "Whenever a Mark awakens successfully, it resonates, causing those around to also awaken it."
It was a precise description found in the records of the Ubuyashiki family.
As Riezel recalled those records, he made a speculation.
"I believe the first person to awaken the Mark is crucial."
"Awakening the Mark shouldn't be easy since there must be some conditions that even I'm unaware of that need to be met. However, once someone successfully awakens it, those around them can more easily awaken theirs."
Of course, his speculation had its basis.
During the Sengoku period, many of the first-generation Demon Slayers within the Corps awakened their Demon Slayer Marks after Yoriichi joined the Demon Slayer Corps.
In the original work, after Tanjirou joined the Demon Slayer Corps and later successfully awakened the Demon Slayer Mark, several Hashira easily awakened it using the method mentioned above.
Apart from the periods when Tanjirou joined the Demon Slayer Corps, the original work did not mention any era in the Corps' history when a large number of Marked Demon Slayers appeared.
With this in mind, Riezel continued explaining his speculation to the Hashira.
"Perhaps the first person to awaken the Mark can only be the user of Sun Breathing or maybe there are other conditions for its awakening."
"In short, once someone successfully awakens the Mark, those around them can successively awaken it due to some resonance."
"According to this speculation, it might be challenging for you to awaken the Mark when no one has done it yet, but the difficulty will probably decrease when one of you successfully awakens it."
Riezel's speculation caused the Hashira to furrow their eyebrows.
"Anyway, just give it a try. First, try raising your body temperature to 39 degrees and increase your heart rate to over 200 beats per minute to see if there are any changes in your body, then decide what to do next."
With Riezel's suggestion, the tense expressions of the Hashira relaxed.
"So, we're going to fight, right?"
Saying this, Sanemi immediately locked eyes with Kyoujurou.
"Do you want me to be your opponent, Shinazugawa?"
Kyoujurou clearly understood Sanemi's intention.
"We still have a score to settle, don't we?"
Sanemi referred to the time when Kyoujurou had just become the Flame Hashira.
In short, they had some disagreements, thus a brief confrontation.
"Umu! I'm fine with that!" Kyoujurou readily agreed.
In the past, they hadn't been able to determine a winner because Kyoujurou didn't want to violate the rules of the Demon Slayer Corps. Fighting against a fellow member, especially a comrade, was forbidden in the Corps, something he naturally didn't want to do out of impulse.
However, now was a different story.
If there was a reason to fight, he wouldn't refuse.
"Good."
Sanemi showed a fierce grin.
At the same time, the other Hashira also prepared for paired combat.
Riezel stepped back a distance, watching as all the Hashira paired off and began their respective battles.