Months passed. Naruto, now nine years old, continued his double life. By day—an inconspicuous average student at the Academy; by night—a fanatical cultivator in the dungeon.
But progress had halted.
The boy sat cross-legged on the cold stone. Before him lay the unrolled scroll of instructions.
He had fully mastered the Early Stage of Body Tempering. His muscles and tendons, saturated with Qi, had become as dense as ox sinew. He could run for hours without losing his breath. Sparring with Kiba, which had once seemed like a challenge, now felt like a game in slow motion.
But he was stuck.
The flow of Qi was no longer growing. He had hit a bottleneck.
No matter how much Naruto meditated, the energy circulated in a loop but did not deepen. It was cramped. It pressed from the inside, causing an unpleasant itch under his skin, as if his body had become too small.
The scroll stated: to advance to the Middle Stage, Qi must penetrate deeper. Through the muscles. Into the bones. Into the bone marrow.
But his skeleton remained a closed fortress.
I feel the barrier... he thought, gritting his teeth. Like water crashing against a stone dam. I push, but it doesn't pass through.
Of course you're stuck, brat, the Fox's voice drawled with lazy mockery. Trying to pierce steel with a drop of water. Pathetic. You spent months on your "little white water," and in the end, you hit a wall.
I will find a way.
There is a way. Right here.
Red, furious chakra surged behind the Seal, washing him in heat.
One word. Ask. I will give you so much power you will burn a path not just into your bones—but through this mountain. Stop wasting your time. How many years will it take at this pace? Five? Ten? Enemies are growing. The Uchiha is growing. Take my power, and you will step over them tomorrow.
There was more than just an offer in the Fox's voice—there was offended pride. It infuriated him that his jailer preferred a weak, strange energy to divine might.
No. Your power is poison. It burns the mind. I must break through myself. Otherwise, I won't be able to control it.
Then break yourself, idiot.
The Kyubi fell silent, retreating into the shadows.
Naruto closed his eyes again, recalling the instructions.
Strengthening the Frame.
This meant one thing: he had to use force, a mental hammer, to drive the Qi through the dense shell of his bones and inside, into the marrow.
Not meditation. Torture.
He took off his old grey t-shirt, crumpled it into a tight ball, and shoved it into his mouth, biting down hard. If he screamed, they might hear him upstairs. He couldn't risk it.
Inhale.
He gathered all the Qi accumulated in his muscles over months of training. Compressed it into a dense ball in his solar plexus. And then directed this ball into his left arm. The breakthrough point.
White energy, dense as mercury, struck the bone of his forearm.
Nothing. The bone didn't yield.
Push!
He tightened his mental vice. The Qi, having no exit, began to vibrate. The pressure grew. His arm began to shake. The periosteum—a thin, sensitive film—stretched to its limit.
And burst.
CRACK.
The sound came from inside his body—wet, crunchy, nauseating.
The pain was as if a red-hot nail were being slowly driven into his marrow.
Naruto arched his back. His jaws clamped onto the rag with such force that his teeth creaked. His eyes flew open, but he saw nothing—a white veil stood before his vision.
Self-preservation instinct screamed: Stop! You're breaking yourself! You're crippling your body!
But he knew: if he stopped, the Qi would dissipate, causing irreparable damage. There was no turning back.
He drove the energy further. Into the elbow. Into the shoulder. Into the collarbone. Into the spine.
Every centimeter of bone tempering was a battle. His skeleton melted and resolidified. Thousands of ice needles pierced his bone marrow, washing away human weakness and replacing it with pure energy.
His bones were being reforged, becoming heavier, denser. Turning from calcium into metal.
Sweat poured down his face in rivulets, mixing with uncontrollable tears. A salty taste of blood filled his mouth—he had bitten through his lip and the fabric.
Look at that... the Fox's voice sounded muffled, as if even the ancient demon was impressed by this madness. You really decided to reforge yourself alive. Stupid, stubborn, crazy brat.
Naruto didn't answer. He was busy trying not to die.
Finally, the wave of pain reached his feet and grounded into the earth. His body went limp. His consciousness, unable to withstand the overload, mercifully shut down.
...
He woke up to silence.
A strange silence. Loud.
Drip...
The sound of a falling drop of water echoed like a grenade explosion. Naruto jerked, covering his ears with his hands.
Scritch... scritch...
Somewhere in a far corner, a rat was skittering. To the boy, it sounded like the stomping of an elephant.
He opened his eyes. The light from the torch lit before meditation cut into his retinas.
Sensory overload.
His body had changed. His nervous system, reinforced by the new structure of bones and marrow, had become hypersensitive.
"Quiet..." he croaked, squeezing his eyes shut.
It took several minutes to calibrate his senses. Using Qi Concentration, he created a mental filter, muffling the incoming signals.
When the world stopped screaming, he could assess himself.
Naruto stood up.
His body ached, but it wasn't the pain of injury—it was a pleasant heaviness. He felt his skeleton. He felt heavier, more stable. As if his bones had been cast from lead.
Broke through. Middle Stage of Body Tempering. Bone Strengthening.
He approached the stone wall of the Sanctuary. Clenched his fist. The sensation was different. His knuckles felt like stone.
Strike.
Not with full force, without a wind-up. A quick, short jab with a pulse of Qi.
THUD!
The sound was dull, dense.
He pulled his hand back. A clear indentation, a centimeter deep, remained on the hard granite. His knuckles didn't even turn red; the skin wasn't broken.
Naruto looked at his hand with awe.
This level... It's no longer the strength of a child. Almost the level of a genin using chakra. But without chakra.
The strength was merely a side effect. The main change lay elsewhere.
He closed his eyes and expanded his consciousness.
The barrier had fallen. Now the Qi circulating in his bone marrow acted as an antenna.
He didn't just "see" the energy inside himself. He felt the world around him.
The vibration of the earth beneath his feet. The heat of the rat in the corner. The auras of people sleeping in houses on the surface, dozens of meters above him. They looked like dim candles in the dark.
The Initial Stage of Qi Sensory.
His world had become bigger.
Now he had a tool to spot the enemy before the enemy spotted him.