The first variable was pain.
It wasn't the dull, throbbing ache of a hangover or the sharp sting of a papercut. It was a structural failure of the mind. It felt as though someone had taken a sledgehammer to my frontal lobe, shattered the bone, and then poured molten lead into the fissures.
I tried to scream, but the command got lost somewhere between my brain stem and my larynx. My mouth opened, inhaling the taste of iron and wet earth, but the only sound that emerged was a dry, rattling wheeze.
Data corruption, my mind supplied. System rebooting.
But there was no system. There was no monitor, no ergonomic chair, no hum of the server room.
There was only the sky—a bruised, violet expanse choking on smoke—and the sensation of cold, viscous mud seeping through the back of a thin hemp shirt.
I blinked. The world didn't stabilize. It fractured.
My vision was swimming in a sea of red static. The input was too high. I could see the dust motes dancing in the air, not as a blur, but as individual, jagged particles colliding with one another. I could see the veins in the leaves of a tree thirty feet away, pulsing with a faint, blueish luminescence.
Visual cortex overstimulation. Error code: Unknown.
I rolled onto my side, retching. My body—this wasn't my body. My hands were too small. The skin was calloused, scarred, and caked in dried blood that wasn't mine. I stared at the fingers, flexing them. The latency was zero, but the proprioception was all wrong. The center of gravity was lower. The muscle density was higher than it should be for a limb this size.
A child. I was a child.
Memories that weren't mine slammed into the forefront of my consciousness like a freight train.
Kira. My name is Kira. Ten years old. Uchiha Clan. Father dead. Mother dead. Third battalion, vanguard support. Mission: Hold the ridge.
Then, the final memory of the previous owner of this flesh: A Senju blade catching the sunlight. A spray of arterial red. The overwhelming, crushing despair of dying before proving his worth.
Soul Shock.
The term surfaced from the depths of the lore I vaguely remembered, but the reality was far more biological. The despair wasn't just an emotion; it was a chemical trigger. I could feel it—a hot, acidic flood of chakra erupting from my brain stem, searing along the optic nerves. It felt like my eyes were boiling in their sockets.
"Get up, you corpse-maggot."
The voice was rough, like gravel grinding on glass.
My analysis kicked in instinctively. Source: Male, approx. 30 years. tone: Derisive, authoritative. Threat level: Moderate.
I forced my head up. Standing over me was a man in lacquered armor, the red-and-white fan of the Uchiha embossed on the breastplate. His face was a map of scars, his eyes cold and dark.
"I said get up, Kira," he spat, kicking me in the ribs.
The impact was a data point. Force: ~400 Newtons. Ribs: Bruised, not broken. Pain receptor response: High.
The old me would have curled up. The new me—the analyst, the one who saw life as a series of resource management problems—did the math. If I stayed down, he would kick again. If he kicked again, he might rupture the spleen. Spleen rupture in a pre-industrial medical setting leads to internal bleeding and death with a 90% probability.
I scrambled to my feet. The movement was jerky, my equilibrium shot.
"My apologies... Gochō-dono (Corporal)," I rasped. The archaic honorific slipped out automatically, pulled from the muscle memory of the dead boy.
The man sneered. "Apologies don't clean blades, boy. You fainted. Like a civilian. Disgraceful."
He leaned in, grabbing my chin with a rough hand. He stared into my eyes, and for a split second, his expression shifted from contempt to shock.
"The Sharingan..." he whispered. "You awakened it? From fainting?"
I pulled away, looking down at a puddle of rainwater collected in a footprint. The reflection stared back. A pale, blood-smeared face of a child. And in the eyes—a single, black tomoe spinning slowly in a pool of crimson.
It wasn't a gift. It was a heads-up display.
The world looked... solvable.
The movement of the wind through the grass wasn't random; it was a vector field. The Corporal's stance—weight shifted to his left leg, shoulder dipped—telegraphed his intention to turn away 0.5 seconds before he did it.
Hypothesis: The Sharingan doesn't see the future. It processes the present with such high-fidelity bandwidth that the brain can extrapolate the most likely outcome based on kinematic physics. It's a predictive algorithm running on wetware.
"Clean yourself up," the Corporal barked, turning his back. "The Senju skirmishers are probing the valley. We move in ten minutes. If you lag behind, I'll leave you for the crows."
"Understood," I said. My voice was flat. Detached.
I looked at my hands again. They were trembling, not from fear, but from the adrenaline dump of the Soul Shock.
Objective: Survive.
Constraints: Child body (low mass, low reach). Limited chakra reserves. Hostile environment.
Assets: 1-Tomoe Sharingan (enhanced perception). Adult intellect (tactical analysis).
Strategy: Optimization.
I realized then that I wasn't the protagonist of a shonen manga. I wasn't going to scream about friendship and punch a god. I was a variable in a math problem written in blood. And I hate failing math.
The Uchiha encampment was less a village and more a factory for death.
Rows of tents sat in the mud, smelling of unwashed bodies, woodsmoke, and the metallic tang of sharpening stones. There was no laughter. No children playing ninja. The children here were sharpening kunai or hauling water with dead eyes.
I sat on a log near the edge of the perimeter, engaging in what Nathaniel Gwyn would call 'resource allocation.' In this case, the resource was my own physiology.
I held a kunai in my hand. It was heavy, poorly balanced, the iron pitted with rust.
Test 1: Chakra Flow.
I closed my eyes and reached for the energy inside. It felt like a secondary circulatory system, hot and volatile. The previous 'Kira' had small reserves, barely enough for three Great Fireball techniques before cardiac arrest.
Inefficient.
If I used standard jutsu, I would die. The Senju were stamina monsters. In a contest of attrition, I lose 100% of the time.
I needed an edge. I needed physics.
I stood up and approached a training stump. I held the kunai in a reverse grip. Standard Uchiha doctrine taught to strike with force—using the shoulder and hip rotation. Force = Mass x Acceleration.
But I lacked Mass. So I had to maximize Acceleration.
I focused my chakra not into the blade, but into the tenketsu (chakra points) of my elbow and wrist.
Hypothesis: If I release a burst of chakra at the exact moment of extension, acting like a hydraulic piston, I can increase the velocity of the strike exponentially.
I visualized the vector. A straight line. Suji (the line of the tendon).
I struck.
Snap.
The sound wasn't a thud. It was a crack, like a dry branch breaking. The kunai buried itself into the hardwood up to the hilt. My wrist screamed in protest, the ligaments strained by the sudden torque.
"Interesting," I muttered, massaging the joint. "Kinetic amplification via localized chakra burst. High stress on the body, but high penetration."
"Talking to yourself, Sessha?"
I spun around. The Sharingan flickered to life instinctively, painting the world in high-definition vectors.
Standing there was a boy, maybe twelve. He had the high collar of the clan, his hair tied back in a short ponytail. He looked at me with the weary arrogance of someone who had survived three winters of war.
"Izuna-sama," I said, recognizing the face from the memories. Madara's younger brother. A VIP.
I bowed low, pressing my hands to the sides of my thighs. The social hierarchy here was absolute. Disrespect meant a beating. Insubordination meant death.
"I heard you awakened the eyes," Izuna said, stepping closer. He didn't look impressed; he looked calculating. "Fainted like a girl, woke up a warrior. Father is amused."
Father. Tajima Uchiha. The Clan Head. Being on his radar was a double-edged sword.
"I am unworthy of Oyakata-sama's attention," I replied, keeping my eyes on his sandals. Deference. Submission. Survival.
"Show me," Izuna ordered. He drew a wooden practice sword. "Strike me."
Risk Assessment:
Option A: Refuse. Result: Izuna takes offense. Beat down. Status drops.
Option B: Fight normally. Result: Defeat. Izuna is stronger, faster, and has more experience. Status drops.
Option C: Cheat. Result:...Variable.
"As you command," I said.
I picked up the wooden bokken leaning against the log. It was heavy.
Izuna settled into a stance—Seigan no Kamae. Balanced. Defensive. He expected me to charge.
I didn't charge. I stood perfectly still, letting the Sharingan read his micro-expressions.
His weight shifted to his toes. Prepare to lunge.
His right shoulder dipped 2 degrees. Rising slash.
I waited.
Izuna frowned. "Well?"
He lunged.
The speed was terrifying. To a normal eye, it would have been a blur. To the Sharingan, it was a stream of data. I saw the Nagare (flow) of his chakra concentrating in his legs. I saw the Ikioi (momentum) building behind the strike.
I didn't block. Blocking absorbs energy. I didn't have the mass to absorb his strike.
I stepped into the arc.
As his sword came up, I applied the principle of Teko (leverage). I didn't strike his body; I struck the hilt of his sword, perpendicular to the vector of his swing, right at the fulcrum point of his grip.
A tiny tap.
But because I hit it mid-swing, the rotational inertia worked against him. The sword twisted violently in his hand. His wrist buckled.
Kuzushi (Breaking balance).
Izuna stumbled, his center of gravity compromised. He was open.
I stopped my bokken an inch from his throat.
The clearing went silent. The rain began to drizzle, cold and indifferent.
Izuna stared at me, his Sharingan (two tomoe, I noted) spinning wildly. He wasn't angry. He was confused.
"You... you didn't overpower me," he whispered. "You barely touched me."
"I merely redirected the Nagare, Izuna-sama," I said, lowering the sword and bowing immediately. "Your strike was powerful. Too powerful. It was hard to stop, but easy to turn."
Izuna straightened up, brushing the mud from his hakama. He looked at me for a long moment, the arrogance replaced by a sharp, predatory interest.
"Kira," he said, testing the name. "You're weird. You fight like an old man."
"I fight to live, Izuna-sama."
He smirked. "Good. Don't die in the skirmish today. I want to see that again."
He turned and walked away.
Analysis: Interaction successful. VIP interest secured. Threat level reduced.
I let out a breath I didn't know I was holding. My hands were shaking again. That "tiny tap" had required precise calculation of torque and angular momentum. If I had missed by a millimeter, he would have broken my collarbone.
I looked at the sky. The clouds were gathering.
"Time to go to work," I whispered.
The skirmish wasn't a battle. It was a slaughter.
We were deployed in a ravine, the mud slick and treacherous. The Senju ambush came from the tree line—a barrage of water bullets that tore through the underbrush like cannon fire.
"Contact! Three o'clock!" someone screamed.
I dropped into a crouch, the Sharingan flaring.
Target acquired.
A Senju adult. Massive. Holding a spear. He was charging straight at me, seeing a child, seeing an easy kill.
I didn't feel fear. I felt the cold, hard clarity of the Focus state.
Distance: 15 meters. Velocity: 8 m/s. Weapon reach: 2.5 meters.
He thrust the spear. A simple, linear attack.
I didn't dodge. I dropped my weight, activating the chakra in my soles to increase friction coefficient, grounding myself.
Equation: The spear is a lever. The fulcrum is his lead hand.
As the tip approached my chest, I slapped the shaft, not away, but down.
Gravity plus my force.
The spear tip drove into the mud. The Senju's momentum carried him forward. The shaft bent, then acted as a pole vault. He was lifted off his feet, his balance destroyed.
Now.
I stepped in. Not a slash. A thrust.
I aimed for the axilla—the armpit. The gap in the armor. The Brachial Artery.
My kunai sank in. Hot blood sprayed over my face.
I didn't pull out. I twisted. Torque.
The Senju screamed, a gurgling, wet sound. He swiped at me, but his arm was already useless, the nerve cluster severed. He fell to his knees, clutching the wound.
I stepped back, panting.
He looked at me, eyes wide with shock. He wasn't looking at a warrior. He was looking at a math problem he couldn't solve.
"Monster," he wheezed.
I looked down at him. I didn't feel triumph. I felt... efficient.
"No," I said softly, wiping the blood from my eyes. "Just a better calculator."
I didn't finish him. I didn't have to. The hypovolemic shock would kill him in 40 seconds. I turned to the next target.
The battlefield was a chaotic swirl of vectors, forces, and trajectories. And for the first time in two lives, I saw the pattern.
I could survive this. I could optimize this.
I gripped my kunai tighter. The pride—the Nathaniel Gwyn pride—burned in my chest. I would eat the rotten food. I would crawl through the mud. I would calculate the trajectory of every raindrop if I had to.
But I would not die.
Begin Tutorial.