Sasuke's interest in a third eye had not begun recently.
It traced back to two years earlier, when he first started studying medical ninjutsu. In this world, the idea was not speculation. The most undeniable proof stood in legend itself: Kaguya Ōtsutsuki and the Moon Eye that once gazed upon the world.
Knowing that such a thing had existed, Sasuke never dismissed the subject.
Through dissection and examination, he confirmed that living beings here were no different from those he remembered studying before. Beneath the forehead lay a dormant structure, a vestigial organ resembling an eye. Humans were no exception. He had verified that much during the Snow Country mission, examining fallen shinobi in silence.
He could not dissect himself, but medical techniques and instruments told him enough.
And yet, the Uchiha were different.
With time and precision, Sasuke could induce that dormant structure to manifest in small animals. Rodents responded quickly. Their bodies were simple. Their resistance was low.
Humans were another matter.
And he himself was something else entirely.
If a mouse required a single step, a normal human required many. For Sasuke, the distance was immeasurable. Not because it was impossible, but because the endpoint was no longer ordinary.
If his third eye were to awaken naturally, it would not be a mere organ.
It would be the Moon Eye.
A power capable of casting all life beneath a single illusion, sparing nothing beneath its light.
That path was not one to rush.
Still, his research had yielded something else.
The Uchiha third eye could not be awakened easily. But it could accept an eye.
A transplanted one.
Sasuke possessed eyes that would never reject him.
His plan regarding Fugaku's Mangekyō had long been settled. Eternal Mangekyō was a matter of method and timing.
Mikoto's Sharingan, however, had remained unresolved.
It was only a three-tomoe eye. Not Mangekyō. Even if evolution were possible, Mikoto and Fugaku were not close enough in blood for direct fusion. At best, he could only choose one.
Using such an eye as a disposable technique was unacceptable. He lacked the means, and more importantly, he rejected the idea itself.
Then there was the problem of placement.
Transplanting a Sharingan into an arm or palm was crude. It wasted the eye's perception, its clarity, its true strength. Sasuke had no intention of repeating such mistakes.
The answer lay at the forehead.
The dormant organ there was surrounded by familiar pathways. Sensory nerves. Channels once meant for sight. And when his Mangekyō awakened, he sensed something else.
A presence.
Faint. Concealed. Small in quantity, yet refined to an extreme degree.
Yin chakra.
Its purity rivaled that of his Mangekyō.
Without medical training, no Uchiha would have noticed it. Even among his clan, few would think to look beyond the eyes themselves.
That realization changed everything.
A Sharingan transplanted there would not be blind. It could open and close at will. In peace, it would remain hidden. In battle, it would awaken without delay.
And because it was a blood-relative's eye, rejection was not a concern.
More than that, the presence of yin chakra meant growth was possible. Not static. Not borrowed power. The eye could evolve alongside him.
One day, perhaps, it could become something more.
Still, Mikoto's eye remained a limitation.
Three tomoe was not enough. The chakra within the forehead was refined, but scarce. Natural evolution would take years. Decades.
And there was another requirement he refused to manufacture.
Emotional collapse.
He would not create another disaster. Not again.
That path was unstable. Dangerous. And unfinished.
So his thoughts turned elsewhere.
To Kusagakure.
To Hōzuki Castle.
And to the Box of Bliss.
A relic attributed to the Sage of Six Paths. Four faces carved in stone. A device said to grant a wish, yet infamous for the price it demanded.
Sasuke knew the truth behind it. Wishes were bait. The reward was real, but limited. What followed was inevitable.
But limits were acceptable.
If the Box could force evolution.
If it could push a dormant Sharingan beyond its boundary.
Then it was enough.
Sasuke closed the file.
The path forward was clear.