Demon Slayer World, Demon Slayer Corps
"Is this... Ninjutsu?"
Rengoku Kyojuro stared at the Fire Release wielded by Sasuke and Itachi, then thought of his own Flame Breathing—
—all show, no real killing power.
The same went for Tanjiro; even with Sun Breathing,
a sweep of his blade produced flames that danced along the edge,
yet they were only for appearance—visually impressive but carrying no true heat.
"Seems so," Tanjiro replied. Though a charcoal-seller, he knew what Ninja and Ninjutsu meant.
In the previous videos, No.4 and No.1 had featured people from that world, but their fights
had mostly shown Kyojuro and Tanjiro the pinnacle of strength over there.
It felt like watching aliens invade Earth—impressive but detached from reality.
In short, ordinary folk could enjoy the spectacle without grasping its essence.
Now, though, the abilities displayed by Uchiha Sasuke and Uchiha Itachi gave Rengoku Kyojuro a glimpse of how their battles actually worked.
"Wouldn't it be nice if we had Ninjutsu? Dealing with demons would be so much easier,"
he sighed, though he didn't believe anyone in their world could learn it—
without Chakra inside their bodies, Ninjutsu was impossible; they could only marvel at another world's might.
Magical Girl Illya World
"Eh, did he just hold back?" Illya noticed the detail, blinking in surprise.
Only minutes earlier she'd viewed Itachi as a terrible big brother.
Illya herself had a wonderful sibling, so she and Miyu shared a rosy image of older brothers.
But Itachi's act of plucking out Sasuke's eyes had shattered that worldview,
and she'd let out a small, anguished cry.
"Yes,"
Miyu answered, eyes fixed on the screen. "Just as the black flames were about to touch Sasuke, this person called Itachi extinguished them."
Though neither girl knew how powerful Amaterasu was, White and Black Zetsu's explanation
made it clear: had those flames landed, Uchiha Sasuke—whose voice resembled an older brother's—would have died.
At this thought, Miyu and Illya exchanged glances; they felt that this so-called 'big brother' Itachi didn't seem as bad as they'd imagined.
In the genjutsu world he had indeed tortured Sasuke relentlessly.
Yet once they were in the real world he appeared to hold back against Sasuke at every turn, while Sasuke fought with everything he had.
These details stood out clearly to Illya and Miyu; after all, they were watching as third-party viewers, so seeing things plainly was only natural.
The video continued to play.
Once Amaterasu vanished, Sasuke froze for a moment, then his expression turned grave—he too had sensed the terrifying power of those black flames.
A gust of wind swept past, and Sasuke half-stepped backward.
'Incredible…' White Zetsu exclaimed, staring at what had just happened. 'He swallowed flame with flame until nothing was left.'
'That jutsu only needs a glance at the target,' Black Zetsu rasped. 'Once the focal point is set, black fire ignites at the spot you're looking at.'
'The black flames won't go out until whatever they catch is completely consumed—even if the thing they're burning is fire itself.'
The moment Black Zetsu finished, the BGM swelled, signalling that the battle had reached its climax.
Sasuke regarded Itachi in silence, then broke into a sprint without a word, racing into the distance.
Itachi stood where he was, watching Sasuke run, and obligingly opened his right eye, blood trickling from it.
Amaterasu surged toward Sasuke, yet whether because he was too fast or for some other reason, the black flames always lagged a step behind.
Instead, the nearby forest and buildings erupted in black fire, exactly as Black Zetsu had said.
Those flames devoured everything; there was no way to stop them.
Sasuke kept running, constantly glancing back, clearly worried about the pursuing flames.
Itachi kept his right eye locked on Sasuke, and the black fire stayed right behind him.
At last the flames caught Sasuke's great fleshy wings; the moment they touched, the wings ignited.
Sasuke screamed in agony, yet oddly, only the wings caught fire—his body remained untouched.
After a short cry he fell silent, as though dead.
Hah… hah…' Itachi shut the Amaterasu in his right eye and, gasping for breath, walked toward Sasuke.
Half of Sasuke's body was charred black; he looked lifeless.
So Itachi wins after all?' White Zetsu muttered, sounding resigned.
Black Zetsu rasped on, 'He's stopped Amaterasu—he must want to take the eyes.'
Looking down at the unconscious Sasuke, Itachi's eyes flickered with disappointment, yet he still reached out to touch him.
Pfft—
The Sasuke in front of him deflated like a punctured doll, turning into a paper-thin shell before dissolving into a puddle of white liquid and vanishing.
Where Sasuke had lain, a crack now split the ground.
Eh?!' White Zetsu exclaimed.
Below!' Black Zetsu added, equally startled.
Down below, Sasuke smiled, dripping wet like some newly-molted creature.
Scenes of moments ago flashed through his mind.
'Injuries like this are still far from enough. I can't use that substitution until that guy brings out Amaterasu.'
Struck by Amaterasu, he had used Chidori to slice open the earth, then sloughed off his old body like a snake, leaving the husk above while he slipped out through the fissure.
Now Sasuke grinned up at the opening. 'I've been waiting for this moment.'
As he spoke, cursed seal patterns spread across him, warping much of his appearance: a cross-shaped mark appeared on his face, and even his skin darkened.
This was the second stage of the Cursed Seal, boosting every aspect of his power.
In that form Sasuke formed a hand seal.