The world of One Piece.
A small boat drifted quietly.
Sunlight spilled across the deck…
Dracule Mihawk pushed open the cabin door and took in a deep breath of sea air.
"Huuuh~~~"
SWISH!!!
In an instant, Mihawk's gaze sharpened to a lethal edge, and a terrifying aura burst forth!
Black Blade—Yoru, unsheathed!!
A razor-sharp slash shot skyward, slicing the clouds in half.
"So that's it… the breathing technique?"
A faint smile lifted Mihawk's lips.
That technique he had just used—he had incorporated the breathing method he saw Tanjiro using in the video.
Of course, simply watching the video wasn't enough to fully master the technique.
But imitating it?
That, he could do.
To his astonishment, this breathing method seemed to stabilize his strikes—making his sword aura and slashes flow more smoothly and more powerfully.
This discovery thrilled Mihawk.
He was a swordsman who pursued strength above all else.
And he was certain—if he could master this mysterious breathing style and adapt it into something that suited him…
His swordsmanship would grow even more formidable.
"Interesting. Very interesting!"
Mihawk's golden eyes gleamed with intensity as he turned his attention back to the transparent screen.
Opening the video, Mihawk began replaying Tanjiro's breathing sequence again and again.
...
The world of Naruto.
Konoha Training Field.
Two figures in identical green spandex and bowl-cut hair were walking on their hands as part of their daily routine.
"Lee!! Come!! Follow my breathing rhythm!!"
Might Guy's eyes shone with excitement.
When he first saw Tanjiro's breathing technique in the video, it felt like a revelation—like cold water poured over his head, awakening something inside him.
He immediately dragged his beloved student, Rock Lee, into special training.
"Huuu~~ I understand, Guy-sensei!!"
Rock Lee, eyes blazing with determination, followed his teacher's breathing rhythm as he continued his intense physical drills.
Internally, Lee was shocked.
When he synced his breathing with Guy's, his body suddenly felt lighter—
Not only that, but it was as if his stamina was being generated continuously from within!!
He had never felt this sensation before.
"Excellent, Lee!! Maintain that rhythm!"
Guy's movements were smooth, precise, and powerful.
Compared to Lee's slight strain, Guy seemed totally at ease—each step maximizing the use of his muscles.
And with the newly imitated breathing method, a steady stream of energy flowed through him.
"Guy-sensei! This is the breathing you mentioned earlier!?"
Lee panted, but his breathing remained steady—making him feel more fired-up than ever.
"Correct, Lee!! This is the breathing technique I mentioned! I haven't grasped its essence yet, but I've mastered the basics. You should be feeling the changes in your body too."
Guy nodded, his eyes burning with fighting spirit as he glanced at the video.
"This young man… is remarkable!!
To master such a refined training method at his age…"
He couldn't help but feel a battle-lust rising.
He wanted… to fight him!
...
The world of Bleach.
Soul Society, Seireitei—First Division HQ.
"This breathing technique must be researched."
Genryusai Shigekuni Yamamoto turned toward Mayuri Kurotsuchi and gave his order immediately.
As a master swordsman, the moment he saw Tanjiro use the breathing technique, his intuition told him—
This technique would have tremendous significance for the power of the entire Shinigami Corps.
Mayuri stared at the video with curiosity.
But once he heard Yamamoto's command, he left the meeting room without another word.
...
Back in the video.
With a sharp pop, the boar mask flew off the boar-headed man's head—revealing a shockingly beautiful face beneath it.
Across the multiverse, countless watchers froze.
Nobody expected that beneath such a wild boar mask…
was someone whose looks rivaled, or even surpassed, a girl's!!
His gemstone-like eyes burned with fiery rage.
[Hahahahaha!! Interesting! You're interesting!! Remember my name!! I am Inosuke Hashibira!!!]
Inosuke ran a hand over his throbbing forehead.
Fresh blood smeared across his fingers.
His forehead had cracked open under Tanjiro's headbutt—blood pouring freely…
Meanwhile Tanjiro—
Everyone stared open-mouthed at his forehead—
Smooth.
Shiny.
Completely unharmed.
He didn't have a single scratch!!!
What kind of skull was this!!?
The difference was just too drastic.
Normally, the one attacking with their head should be the one getting hurt!
So why…
Why did Tanjiro look like nothing happened to him at all!?
Across the multiverse, countless people unconsciously touched their own foreheads.
In their minds, they replayed Tanjiro's furious headbutt—
And trembled.
Quietly swallowing hard.
The Head-butt Hashira—
truly terrifying.
The screen dimmed once more.
And from the darkness, new text slowly emerged:
[Mugen Train Arc…]
The screen lit up again.
The first thing viewers saw was the familiar face of the Head-butt Hashira—Tanjiro.
But he appeared to be asleep, slumped over the sofa inside a train compartment.
In front of him, a young girl with a bamboo muzzle—Nezuko—was anxiously tugging at her brother's arm.
No matter how hard she tried, Tanjiro remained deeply asleep, unresponsive.
Tock! Tock! Tock!
Strange tapping sounds echoed from somewhere off-screen.
Hearing the noise, Nezuko looked even more distressed.
She shook Tanjiro desperately, but he still didn't react at all.
[Mmm… mmm!!]
The muzzled girl whimpered anxiously—
And then did something no one expected!!
BAM!!!
Across the multiverse, countless jaws dropped.
Eyes went wide in shock.
The bamboo-muzzled girl—
With a forehead as pale and smooth as porcelain—
Had headbutted Tanjiro's forehead!!
[Mmm…]
Her tiny whimper revealed her pain—
But her courage stunned the multiverse.
She was truly… a brave one.