What exactly was Mental Overdrive?
In simple terms—it was a heightened state in which the brain's processing speed surged far beyond natural limits, launching the user into an intense, hyper-focused mental frequency.
The technology behind it was a form of black science from the future. As for how it actually worked… Renjiro didn't know. Even though he came from the year 2300, he had been a nerd, not a scientist or an engineer.
He only understood one thing: activating Mental Overdrive required exceptionally strong mental resilience. Without it, the sheer strain could shatter a person's consciousness—frying their mind completely.
Fortunately for Renjiro, he had what it took to withstand it.
Maybe it was the innate strength of this body's spirit. Or maybe it was the side effect of two souls—his and the original owner's—merging into one. Either way, the moment Mental Overdrive activated, his perception of time changed dramatically.
The wind froze. Leaves suspended in midair hung like ornaments. Tree branches swayed at a crawling speed. Even dust drifting through the air seemed frozen in place.
"Let's see you dodge this time." The Mist-nin teenager said sarcastically as he moved toward Renjiro, completely unaware of what was unfolding inside Renjiro's mind.
With a twisted grin, he drew his kunai—not to kill, but to scare. He wanted to savor the moment. To break Renjiro slowly, to humiliate him before the final strike.
Unlike the other Great Ninja Villages, the Hidden Mist Village had a notoriously brutal training system. Their young were forged through cruelty.
Before earning the title of shinobi, they had to survive a blood-soaked rite of passage. That upbringing twisted many of them, turning them into ruthless, bloodthirsty predators—especially toward outsiders.
"Very slow…" Renjiro muttered under his breath. To him, the kunai seemed to move in slow motion.
Whoosh!
Renjiro tilted his head slightly to the right. The kunai brushed past his cheek and embedded itself into a tree behind him.
Thunk!
"What the hell?" The Mist-nin's eyes widened in disbelief. That had to be a fluke. There was no way a rookie like this could dodge his attacks twice in a row.
"Maybe you're just lucky. Or maybe you've got some hidden strength." The Mist-nin sneered, stepping forward with a murderous glint in his eyes: "But that won't change a thing. I'm going to kill you—right here, right now."
He licked his lips and began walking toward Renjiro, brandishing his kunai. His pace was slow and deliberate—like a predator savoring the final moment before the kill.
Bang!
Renjiro, still slumped against the tree branch, didn't move. His body appeared frozen in fear, his body looked completely limped, and his breathing was shallow.
But inside, his mind was like a storm—racing faster than ever.
Fear had long since burned away, replaced by something far sharper. Adrenaline surged through his veins, sharpening his thoughts into blades. There was no room left for panic. Every twitch of the Mist-nin's muscles, every flicker in his eyes, every subtle shift in posture—Renjiro saw it all in real time.
He knew he couldn't overpower this monster—the product of the Mist's brutal Blood Mist doctrine.
So he wouldn't try a direct confrontation because he would definitely lose. This had to be clean and swift, one opportunity, one strike.
Kill or be killed. There was no second chance.
The Mist-nin reached out, dragging the tip of his kunai toward Renjiro's cheek—clearly intending to carve a scar first. He was toying with him.
"It's now!" Seeing the opening in Mist-nin's posture, Renjiro knew his opportunity has came.
Bushhh!
In an explosion of motion, Renjiro shot up from the ground, tilting his head away from the kunai just in time. His hand darted to his ninja pouch, drawing his own kunai in a flash. He twisted and drove his kunai straight into the Mist-nin's chest.
"Shhk—!"
The sound of metal puncturing flesh tore through the silent atmosphere like a shriek.
The Mist-nin's eyes went wide in disbelief: "You—how—!"
He couldn't finish his sentence, before his body slackened and fell down to ground like a sack of meat.
Thunk!
Renjiro shoved the corpse aside, watching it hit the forest floor with a dull thud.
"Ahh… ahh…" Suddenly he collapsed to his knees, gasping for air, and he was completely drenched in sweat.
With a final breath, he disengaged the Mental Overdrive protocol.
"Damn it... I'm exhausted…" The backlash came instantly.
A tidal wave of fatigue slammed into him. It felt as though molten lead had been poured into his brain.
"So this… is the price… of using Mental Overdrive..." He stared blankly at the fallen body of Mist-nin. A strange stillness settled over him.
"I… killed someone." He whispered in low and conflicted voice, as he looked at his trembling hands.
He had expected guilt, maybe nausea, or horror, but none of that came. Instead, there was only a cold, bitter clarity in his heart.
Because deep down, he knew—if he hadn't killed the Mist-nin, he'd be the one lying dead.
"No time to think about this now. Maemon… Meri—they could be in the same danger!"
Renjiro clenched his fists, forcing his weary legs to move. Then, with a grunt of effort, he launched himself southward—toward the direction Meri had fled.
His decision to help her wasn't driven by sentiment, or the fact that she was a girl, but because it was the most logical choice.
Maemon was clever, resourceful, and cautious. If anyone could survive a surprise attack, it was him. Seri, by contrast, was more spirited—hotheaded, even—and more importantly, she was closer.
---
About ten minutes later
Renjiro reached a towering tree and climbed it with ease. From the top, he scanned the battlefield below—
What he saw nearly made him lose his footing and fell to the ground.
"She's… stronger than I expected." Renjiro thought, his eyes filled with shock.
Meri wasn't struggling like he'd imagined. In fact, the scene below was the complete opposite of what he had prepared himself for.
Wielding her custom-forged short blade, Meri moved with fluid precision. She darted across the forest floor like a wolf on the hunt—slashing, striking, pressing forward without pause. Her opponent, a Mist-nin, was clearly on the defensive. His footwork was focused entirely on evasion and blocking.
"…The hell?!" Renjiro gaped in disbelief.
His eyes drifted downward—momentarily lingering on Meri's more-than-impressive chest.
Although it looked like Meri was controlling the flow of the battlefield, Renjiro's instincts told him otherwise—he could sense that something wasn't right.
"There's something off about this guy." Renjiro narrowed his gaze, watching the Mist-nin more closely.
Though it looked like Meri was winning, the opponent's defense was too clean. His movements were efficient, his expression calm. There were openings—but they were calculated, and he didn't look the least bit rattled.
"He's stalling." Renjiro realized, his expression instantly darkened: "He's waiting for Meri to burn out."
It was a smart strategy. Let the aggressive opponent waste their energy, then strike when their guard drops. Brutal—but effective.
A faint smirk tugged at the corner of Renjiro's mouth: "Good plan... but unfortunately, you miscalculated."
He steadied his breath, letting the familiar surge of power flood back through his veins.
"Arkain—Reactivate Mental Overdrive." He commanded inwardly.
[Beep! Mental Overdrive is Activated.]
Time slowed once more, but this time, Renjiro wasn't prey. He was the hunter—poised, calm, waiting for his moment to strike.
As he analyzed the movement below—the ebb and flow of the battle—a thought crossed his mind.
Mental Overdrive was a boring name. What this ability truly gave him was more than just faster thinking. It let him see—anticipate movement, predict reactions, feel intention.
It let him read the fight before it even happened, kike… Observation Haki.
A wide grin spread across Renjiro's face: "Arkain, rename 'Mental Overdrive' to 'Observation Haki.'"
[Beep! Confirmation received. Ability reclassified: Mental Overdrive → Observation Haki.]