The Price of the Single-Eyed Mangekyo Sharingan and Yang Release

The pain had not yet subsided when an intense itch surged up from inside his eye socket.

The red Sharingan intertwined with Naruto's optic nerve, strand by strand.

His right eye, which had previously seen nothing but darkness, suddenly lit up.

His vision had returned, and it was vastly sharper than before. Everything before him seemed to move half a beat slower, as though he had entered bullet time.

"The Uchiha are so good with shuriken because they're cheating with these eyes."

The images from his right eye left him clicking his tongue in amazement.

After the shuriken left his hand, its trajectory moved so slowly in his vision that it seemed frozen, inching forward bit by bit.

With a flick of his fingers, Naruto sent a second kunai flying after the first.

With a crisp clang, the two kunai bounced apart and embedded themselves on either side of the target.

His brows furrowed.

His dynamic vision had improved too drastically. His body could not keep up with what his eyes saw, leaving his limbs uncoordinated.

Itachi Uchiha had suffered from the same problem when he sparred with Shisui.

"I'll need time to get used to it."

Naruto muttered as he stared at his hand.

He had a much harder time adapting to this Sharingan than Itachi Uchiha had.

Only one of his two eyes was a Sharingan, and the difference in vision between his left and right eyes was unbearably uncomfortable.

That was why Kakashi always kept half his face covered.

After the transplant, chakra began pouring into the Sharingan without pause.

Naruto estimated that it consumed roughly one percent of his total chakra.

This much consumption... was not even as fast as his own recovery rate.

He tried forcing more chakra into it.

The three tomoe within his eye socket began spinning wildly, faster and faster, until they became a large quadrilateral pinwheel in the blink of an eye.

The Mangekyo Sharingan had opened.

Its chakra consumption immediately increased by more than tenfold.

Naruto currently had around ten cards' worth of chakra. At this rate, he could last half an hour at most.

Once the Mangekyo Sharingan opened, his dynamic vision did not improve further. Instead, a searing, blurry sensation burrowed deep from his eyeball.

Naruto did not panic.

Sure enough, a power completely unlike ordinary chakra slowly flowed into his eye through the channel opened by the Mangekyo Sharingan.

That burning sensation gradually faded as the power washed over it.

Asura's Yang Release Chakra.

A special chakra specifically used to repair the body.

Naruto understood everything now.

Whenever Itachi Uchiha activated his Mangekyo Sharingan, bloody tears would flow like they were free within less than ten minutes.

Without Yang Release to protect them, the Mangekyo Sharingan's erosion of the eyeballs could not be healed at all.

As for why replacing one's eyes with a biological brother's Mangekyo Sharingan could stop the damage, he had never understood it before.

The Second Hokage had explained in the anime that the Sharingan was an ocular mutation caused when special chakra generated by intense stimulation in the brain acted upon the optic nerves. They were eyes that reflected the soul.

Naruto knew that this special chakra was the Yin Release Chakra within Indra's bloodline.

He figured that the Yin Release Chakra produced by that special organ connected to the eyeballs was simply not enough to sustain the Mangekyo Sharingan.

Once a relative's Mangekyo Sharingan was transplanted and fused, the organ in the brain responsible for producing ocular power and Yin Release Chakra effectively doubled in function.

When the Eternal Mangekyo Sharingan opened, ocular power surged while the burden on the body decreased. That was the reason.

That also explained why Second Pillar and Itachi Uchiha could not simply exchange eyes and both awaken the Eternal Eye.

Eyeballs could be exchanged, but each person only had one chakra-producing organ. Only by fusing the two could they produce the Eternal Mangekyo Sharingan.

Moreover, the Eternal Eye was not guaranteed to awaken. The closer the blood relation, the greater the chance of success.

Only when the bloodline was close enough would the organs behind the eyes not reject one another, making fusion easier.

Obito and Naruto used the Mangekyo Sharingan in a far cruder way. They simply relied on their powerful Yang Release Chakra to forcibly repair their eyes whenever they were damaged.

With the Mangekyo Sharingan fully activated, the ability of Naruto's right eye, Kotoamatsukami, also flowed directly into his consciousness.

It released a large expanse of golden light from the right eye, dragging the enemy's mind into a genjutsu space where their consciousness could be burned to ashes in an instant.

What excited him even more was that Shisui's Susanoo had already been developed to the terrifying third stage.

Unfortunately, with Naruto's current strength of ten cards, he could not release Susanoo at that stage at all.

At present, he could at most control the half-body skeleton Sasuke had used against Danzo, the first stage, and even that had to be measured in seconds.

This was most likely because he was missing one eye.

Obito had already blazed the trail before him. A Single-Eyed Mangekyo Sharingan was much weaker than a pair, yet consumed chakra even more fiercely.

Naruto could feel that trying to use Susanoo with a Single-Eyed Mangekyo Sharingan would consume an utterly ridiculous amount of chakra.

Even so, the benefits brought by the Sharingan had already far exceeded his expectations.

The time ahead would be the period when he truly built up his strength.

Naruto tossed and turned all night without closing his eyes once, far too excited to sleep.

The next day, his alarm rang nonstop.

He sprang out of bed, covered his right eye with an eyepatch, and began another day of taijutsu training.

He would start by testing Might Guy's Strong Fist to see how useful this eye really was.