"How exactly should I build up power?"
After mastering the Wind Breathing technique to its peak, Umino Yoru continued his training in the secret art of the Konoha Style: Willow—the Iaido slash.
The core philosophy of the Iaido slash was a single, lethal strike—using an ultra-high-speed draw to deliver a fatal blow in an instant.
But to achieve that blinding speed, the key lay in building power.
At this moment, Umino Yoru stood with his right hand resting on the hilt of his Samehada-inspired blade, eyes closed, focusing. He recalled the explosive cutting techniques taught by Maruboshi Kosuke, searching for that elusive, almost mystical sensation.
Yet, something always felt just out of reach.
Shiiing!
A flash of cold light cut through the air.
Umino Yoru drew his blade in a burst of movement, effortlessly slicing through a massive tree ahead.
"What am I missing?"
He shook his head, his frustration growing. Though his swordsmanship had visibly improved, he couldn't achieve that qualitative leap—the true essence of explosive power.
Maruboshi Kosuke had spoken of it in cryptic terms: "You must train endlessly, refine your senses, and seize that fleeting moment of energy to break through."
But this uncertainty was maddening. It tested his patience to the limit.
"Maybe what I need to train isn't just my sword technique… but my state of mind?"
The realization struck him like lightning. This relentless cycle of slashing and refining wasn't just about the blade—it was about tempering his spirit.
Like a blacksmith forging steel, he had to purge the impurities in his heart, honing this single strike into something pure.
And purity… was power.
"Hah…"
Umino Yoru exhaled softly, clearing his mind of distractions. He sheathed his blade, closed his eyes, and began building power again, searching for that explosive sensation.
But before long, an itch crept up his leg—ants were crawling over his feet. The fallen tree had crushed an anthill, sending its inhabitants scattering in chaos.
"Ants?"
His gaze fixed on the tiny creatures, and suddenly—inspiration.
His vacant eyes sharpened, gleaming with newfound clarity.
"The fastest attacking creature on Earth… wasn't it the Odontomachus bauri trap-jaw ant?"
Memories of his past life flooded back, crisp and vivid. If his old-world science books were correct, the trap-jaw ant's mandibles could snap shut at 132 meters per second—faster than a bullet train.
But the truly terrifying part?
Its acceleration reached 1.7 million m/s²—over 177,755 times the force of gravity (G).
"What does that even mean?"
An average adult weighed around 50 kg. At 1G, that's 50 kg of force. At 2G, 100 kg.
But 177,755G?
That would be 8.8 million kilograms of force.
"Could even Might Guy's final kick reach a million kilograms?"
Honestly, even a fraction of that would be enough to shatter the sky.
Of course, human flesh and bone could never endure such forces. Even standing still, most shinobi would collapse under 10G, let alone 177,755G.
So how did the trap-jaw ant do it?
Its secret lay in stored mechanical energy—the interplay of static and kinetic friction, and the instantaneous release of elastic potential energy.
"Mechanical energy… kinetic and potential…"
His mind raced.
In physics, kinetic energy came from motion, while potential energy was stored—like a compressed spring.
And the two could convert into each other.
"Bingo!"
He snapped his fingers—literally.
The fastest human movement? A finger snap. At 7 milliseconds, it was 20 times quicker than a blink.
And why?
Because the thumb and middle finger acted like a spring, storing potential energy before releasing it as kinetic energy in a split second.
The same principle applied to sprinters—they coiled their bodies like springs before exploding forward.
"So… the 'power buildup' isn't in the sword. It's in the body*."*
The epiphany hit him like a tidal wave.
To maximize his Iaido slash, he didn't need to focus on the blade—he needed to treat his entire body as a spring.
Build potential energy in his muscles, tendons, and bones.
Then, in an instant—release it all into motion.
"Hah…"
Umino Yoru took a deep breath, finally understanding. He closed his eyes, hand resting on his blade, and began gathering energy anew.
This time, his mind was a blank slate. No distractions.
He envisioned his body as a human-shaped spring—compressing, coiling, storing power in every fiber.
His stance shifted subtly, knees bending slightly, heels lifting. Like a tiger poised to strike, he was perfectly still yet brimming with lethal potential.
His aura receded, as if every cell in his body had condensed into pure tension.
Then—
A soundless snap echoed in his mind.
SHING!
A streak of silver light—faster than thought—cut through the air.
The boulder ahead split cleanly in two, its cross-section smooth as a mirror.