The vision ended.
Shiro Akira stroked his chin, gloating slightly. "So that was the Demon Slayer world? Interesting… That guy Kaigaku—he's Zenitsu's senior who betrayed the Demon Slayer Corps and joined the demons, right?"
"Tsk tsk… what a miserable end."
He got completely screwed over.
Shiro Akira remembered that in the original timeline, Kaigaku successfully became a demon, even rising to the Upper Moons, and indirectly caused his master's suicide out of guilt.
But now—
Everything had changed because of him.
"Well, that's even better. I don't feel guilty at all. Just a scumbag getting what he deserved."
Just as he was thinking this—
A blue crystal etched with lightning patterns appeared midair and dropped into his hand.
At the same time, information surfaced in his mind:
[Kaigaku Crystal]: A crystallization containing the Thunder Breathing experience and cultivation of the traitor Kaigaku.
(In the original timeline, Kaigaku would transform Thunder Breathing into a black lightning style suited to him after becoming a demon—but he died before that could happen.)
"As expected!"
Shiro Akira's eyes lit up. "So the loss of his cultivation and physique was what caused his failure to become a demon. Nicely done!"
Without hesitation, he followed the usage instructions and tossed the crystal into his mouth.
The moment it entered—
It melted instantly and fused into his body.
Warmth spread throughout him as his muscles, bones, and tendons were rapidly strengthened.
At the same time—
A complete set of Thunder Breathing techniques and corresponding swordsmanship flooded his mind.
Along with it came Kaigaku's years of training experience.
It felt as if Shiro Akira had personally practiced everything himself.
In an instant, he fully mastered it.
Soon, the enhancement process ended.
Shiro Akira clenched his fist. "This feels amazing… My physical strength has at least doubled."
Not only that—
His body now felt perfectly conditioned, capable of executing Thunder Breathing techniques with flawless precision.
"Let's test it out."
Without hesitation, Shiro Akira left his house and headed to his hidden training ground.
This wasn't the river anymore—that place was still under the surveillance of Hiruzen Sarutobi's Telescope Technique.
This new location was safely outside its range.
"Ha…!"
Drawing the finely crafted sword given to him by Sakumo Hatake, Shiro Akira exhaled slowly and began controlled breathing.
White mist formed around his mouth.
"Thunder Breathing—Second Form: Rice Spirit!"
In an instant—
He moved like lightning, slashing five times at five trees in front of him.
Then—
He sheathed his blade.
Crack! Crack! Crack!
Five sharp sounds echoed.
Moments later, each tree trunk split diagonally and began sliding apart before collapsing.
"Boom!"
A loud crash followed, kicking up dust and scattering branches and leaves everywhere.
Shiro Akira had to step back several meters to avoid the falling debris.
"Tsk… that power. Not bad! Let's try the others."
"Thunder Breathing—Third Form: Thunder Swarm!"
In just one or two breaths, Shiro Akira turned into a streak of lightning, attacking a single tree from multiple directions simultaneously.
"Boom!"
When he stepped back—
The tree exploded from the middle, its core reduced to blackened dust.
"Not bad."
"Fourth Form: Distant Thunder!"
…
"Fifth Form: Heat Lightning!"
…
"Sixth Form—"
…
One after another, Shiro Akira executed the remaining six forms of Thunder Breathing.
Every movement felt completely natural.
There was no awkwardness, no hesitation.
His body flowed perfectly with the techniques.
Combined with his enhanced physique and the affinity granted by the Rumble-Rumble Fruit, the techniques felt incredibly smooth—almost effortless.
"Kaigaku couldn't master the First Form… but that doesn't mean I can't."
Shiro Akira smirked.
He sheathed his blade again, gripping the hilt in a draw stance, leaning forward.
"Ha—!"
He inhaled sharply.
White mist gathered once more, and blue lightning began crackling around his body.
Unlike the visual effects in the Demon Slayer world—
This was real lightning.
"Thunder Breathing—First Form: Thunderclap and Flash!"
Crackle!
In the next instant—
Shiro Akira became a bolt of lightning, shooting forward over ten meters.
His blade flashed out, piercing straight through a tree.
The lightning faded.
He appeared behind it, slowly straightening up and sheathing his sword.
Turning back—
There was a fist-sized hole through the trunk.
The edges were completely charred.
Shiro Akira grinned. "Just as I thought. I'm not that useless Kaigaku—of course I can use the First Form."
"Now… let's see what happens when I combine this with my lightning abilities."
"Rumble-Rumble Fruit… Lightning Mode… and pure lightning chakra as well."
"Let's test them all."
Without hesitation, Shiro Akira began experimenting further.