The Demon Slayer Mark
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In the universe of Kimetsu no Yaiba, it represents both the pinnacle and the limit of breathing styles.
This supernatural mark is essential for a demon slayer hoping to defeat an Upper Moon without facing certain death.
Dōma recalled that fans of the KNY manga often created two types of power rankings for the Hashira.
The first was nothing special.
But the second specified: without the Demon Slayer Mark.
That small detail alone showed just how much the Demon Slayer Mark amplified an individual's overall strength.
'Indeed, the Demon Slayer Mark creates a nearly insurmountable gap between those who have it and those who don't…' he thought, glancing at his forearms.
According to Dōma's analysis, a demon slayer undergoes three qualitative changes.
The first is the ability to use a breathing style.
After six months of intense training, a kid like Tanjiro could slice a boulder in half using only his breathing style.
A terrifying feat… but pathetic in the grand scheme of this world.
After all, the Demon Slayer Corps boasts countless users of breathing styles.
Even Dōma's monastery currently housed about a hundred.
This demonstrated just how fearsome the Demon Slayer Corps was within the slightly supernatural context of this fictional world.
In Dōma's view, they were competent enough to hold their own without shame against fictional worlds like Dandadan or Jujutsu Kaisen.
Aside from cursed spirits on the level of Jōgō or the evil eye above, they could be a feared and respected organization in both universes.
The second change comes after the first—simple in theory, but brutally difficult in practice.
It's Total Concentration: Constant.
At this stage, a demon slayer becomes the elite of the human race, a true monster to any demon below the rank of Lower Moon.
This second change also marks the divide between cannon fodder and a Tsuguko.
A Tsuguko only needs a bit more experience to become a full-fledged Hashira after their mentor's death or retirement.
By contrast, an ordinary demon slayer must reach the rank of Kinoe and defeat fifty demons—or one of Muzan's Kizuki.
The task is daunting, especially since they might encounter a demon like the current Enmu.
A demon equivalent to a Lower Moon but not promoted due to its peculiar personality.
Beyond these two changes, there are auxiliary abilities, like detecting the thread leading to a perfect decapitation or rapid recovery through breathing.
'After these two levels comes the ultimate pinnacle of breathing styles: the Demon Slayer Mark.'
Obtaining the mark is lethal if the individual isn't sufficiently prepared.
A demon slayer must reach 200 heartbeats per minute and a body temperature above 39°C (102.2°F)—a deadly situation for a human.
However, for a demon like Dōma, who uses a breathing technique, simulating these conditions is easy.
And yet…
'I couldn't unlock the mark without help, despite knowing this,' he thought, a bitter smile crossing his face.
Back then, Dōma had speculated that the world itself was preventing him from unlocking the Demon Slayer Mark.
Without arrogance, he knew he was a genius—no less than Muichirō, in his own estimation.
Thus, Dōma concluded that some external interference was blocking his progress toward the mark.
An absurd thought, perhaps… but later, the System spoke to him about causality, confirming his suspicions.
The world of KNY didn't want another demon bearing the Demon Slayer Mark.
But Dōma managed to bypass that rule, thanks to Kokushibō.
"D-Dance? What do you mean?" Gyutaro asked, completely thrown off by the turn of events.
The pace was too fast for his brain to keep up.
First, his benefactor had turned into a child.
Then, he learned that said benefactor was an immortal with a taste for human flesh.
And now, he wanted to… dance?
'I need help…' he thought, scratching his head carelessly.
"The time for talking is over, my dear Gyutaro. But first…"
Dōma grabbed the table and hurled it violently toward Mori.
The young Hashira sliced through the furniture with a deft swing of his sword.
"Grave mistake, little ant…" A disapproving voice echoed before Mori's field of vision was entirely eclipsed by a fist.
"Sh—" Mori didn't have time to finish his curse before a punch to the face sent him flying out of Dōma's quarters.
A tooth flew through the air, but no one paid it any mind.
The ice demon pulled out a fan, covering half his face as a fake smile slowly spread across it.
"It's been a while… since I last used a real punch in a fight," he said, his voice tinged with nostalgia.
As he spoke, Dōma casually raised his fan to block a strike from behind.
Bam!
Dust kicked up from the impact, but the ice demon remained unfazed.
Sparks flew from the clash between Gyutaro's sickle and Dōma's fan.
"Hmm… 5 out of 10. But that attack gets a 4. Want to know why I scored it so low? Congratulations, at least you followed my advice: don't shout the name of your technique during a sneak attack," Dōma said, sliding Gyutaro's sickle downward as the latter tried to strike with his second blade.
Due to the excessive force he'd put into his sickle, Gyutaro momentarily lost his balance when Dōma redirected that pressure.
'He probably wanted to bridge the gap in raw strength between us, but he focused too much on power and forgot technique,' Dōma analyzed coldly, maintaining a nonchalant expression.
"Winter Breathing Style—Third Form: Snow Angel's Ascent!" Dōma's second fan swept upward from below at blinding speed.
Even without the support of his Blood Demon Art, this technique could kill.
Why use such a dangerous attack on Gyutaro? Simply because Dōma had faith in Gyutaro's innate talents.
If he died? Well, then he wouldn't have been worth Dōma's time anyway.
"Wind Breathing Style—Third Movement: Clear Storm Wind Tree!!"
Gyutaro spun like a small tornado, countering and attacking simultaneously.
"7 out of 10. But you're still too predictable," the ice demon said, his tone disapproving.
Dōma deflected another attack, this time from a blind spot.
"What do you think? I've SEEN all your techniques, I've studied your fighting styles, and I KNOW all your habits." He didn't say "weaknesses," deeming it too antagonistic.
But it was true—Dōma knew everything about those under his roof.
'The old Dōma had an exceptional memory, which I can use to anticipate attack patterns thanks to my past use of Vanity's Paradise,' he thought to himself.
After these words, Dōma spread his legs slightly and assumed a visually peculiar stance.
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It was the stance of the Tessenjutsu style, which he had created based on its most widespread form.
"*Cough*… G-Gyutaro… we need to work together!"
Mori gritted his teeth as he spoke. He'd realized after taking Dōma's punch to the face that his father had gone easy on him.
If Dōma had wanted to kill him, he would've done so in their first exchange.
'I let my guard down because of my faith in wisteria… Did I rely on an external force again?' Mori clenched his teeth but resolved to return to the fight.
This realization proved that the young sect leader could still temper his pride—and learn.
"Work together? Tch! I wasn't on board with your idea to dig into Dōma-sama's private life, you know!" Gyutaro protested, raising both sickles.
The two men stood united against the one who had once raised them.
"Okay~ I see you're more focused now. *Breathe*…"
As a demon, Dōma had incredibly precise control over his breathing and body.
With this mastery, he could accumulate vast amounts of oxygen and unleash explosive force instantly.
"Winter Breathing Style—Second Movement: Close Combat."
As the name suggested, this technique wasn't designed to decapitate an opponent but for relentless close-quarters combat against demon slayers.
"So fast—"
Mori barely had time to block Dōma's fan.
He didn't even have a chance to breathe for a counterattack before a brutal kick to his shin left him gasping in pain.
"Wind Breathing Style—Fifth Movement: Cold Mountain Wind!"
Gyutaro intervened with precision, but Dōma didn't back down from the storm of blades descending upon him.
The Wind Breathing Style, though versatile like Water Breathing, was far more aggressive than fluid.
Dōma chose to meet the attack head-on. Fans and sickles clashed at breakneck speed—neither side yielding an inch.
"What's going on?"
"Why is Dōma-sama attacking the sect leader and that other guy?"
"I always knew that guy's rudeness would get him in trouble… tch."
The last follower clicked their tongue after their remark—probably at the worst possible moment.
Dōma immediately sensed Gyutaro's aggression spike.
Much like a certain character who grows stronger due to an inferiority complex.
"This isn't Lookism, young man," Dōma said calmly, deliberately taking a blade before grabbing Gyutaro by the collar and slamming their skulls together.
The impact reverberated through the air, but Dōma wasn't done.
He fully intended to knock Gyutaro out.
"Flame Breathing Style—Ninth Movement: Rengoku!!" Mori's low voice rose sharply on the final word.
Demon slayers often shout or announce their attacks because they need to visualize them to execute them.
An inconvenient habit when attempting a sneak attack.
'Kamiya Rengoku…' A silhouette overlapped with Mori's.
Dōma felt as though he were seeing that man through his son… but he refused to let emotions sway him.
With a motion free of excess, he hurled Gyutaro's dazed body toward Mori.
Was it a cowardly act? Perhaps. But history would only remember Dōma's version of events if he won.
Caught off guard by the unexpected situation Dōma had created using Gyutaro, Mori was forced to halt his charge, grimacing as his broken leg gave out beneath him.
"Another mistake… You should've bet on me, idiot~"
Dōma's voice echoed as his palm filled Mori's field of vision.
Mori and Gyutaro ended up face-first in the dirt.
'If he'd bet on the fact that I'd never truly endanger his or Gyutaro's lives, his Rengoku attack might've landed.'
Dōma glanced at his shoulder.
Gyutaro's nichirin sickle was deeply embedded in it, but he pulled it out nonchalantly.
"He got lucky I was too busy with the sun, or else…"
He would've simply shattered the nichirin blade with his vector manipulation before knocking them out with a flick of his fan.
That day, Dōma made a simple decision: avoid fighting humans in broad daylight.