The thought lingered too long.
For an instant, a sharp curve touched Sasuke's lips. The smile was thin, wrong, almost feral. A breath later, it vanished.
He steadied himself.
Since merging with that fragment of himself, his mind no longer stayed perfectly still. When alone, everything dulled. In battle, something darker pressed forward, eager and violent. During the Snow Country mission, it had nearly slipped free. The ease with which his opponents broke had felt… intoxicating.
He had stopped himself in time.
No one on Team Seven had noticed.
Sasuke frowned slightly and returned to the problem at hand.
If he opened the Box of Bliss, the creature called Gō would still emerge. That much was certain. The difference would be its eyes. If his assumptions were correct, this Gō would awaken with Mangekyō Sharingan.
He cut the thought short before it wandered further.
Instead, he reviewed what was known.
In recorded encounters, Gō displayed two defining traits. One was perception. Hostility, fear, intent, even fleeting emotion. All of it was sensed before it could take form. A manifestation of Yin Release, refined to an extreme.
The other was immortality.
At first glance, it resembled Yang Release regeneration. But Sasuke knew better. It mirrored a forbidden Uchiha technique. Reality overwritten. Injury denied. Death converted into illusion.
Izanagi.
No matter how devastating the blow, the result was the same. Gō returned unharmed. Even Hashirama Senju could not replicate such restoration.
There were other signs.
The Box itself bore four faces. Joy. Rage. Sorrow. Pleasure. Emotion carved into stone. In the shinobi world, emotion and mind were inseparable. Where one gathered, Yin Release followed.
In past records, Gō had fought a fully transformed Eight-Tails head-on while enduring coordinated assaults from Konoha's elite. He was never cornered. The Box, too, had resisted every attempt to destroy it. Even sage-enhanced strikes left no mark.
If the legends were accurate, then the Box of Bliss was not merely an artifact.
It was a Yin Release relic of extraordinary rank.
Perhaps second only to the Sage's most sacred tools.
That would explain everything.
If the Box truly embodied such power, then forcing a Sharingan to evolve was not unreasonable. More than that, the immortality it conferred suggested permanence. A Mangekyō born through the Box would not degrade. In practice, it would resemble an Eternal Mangekyō.
Its limits were unknown.
But abilities like mind-reading and reality denial alone surpassed any ocular power he had seen recorded.
There was another advantage.
The Box fed on emotion.
Since the fusion, Sasuke's darker impulses no longer faded on their own. Bloodlust. Obsession. Desire. They surfaced endlessly unless restrained. If the Box absorbed such things, then those excesses could be redirected. Not suppressed. Consumed.
If a third eye born of the Box truly existed, then the more intense his killing intent became, the stronger its Yin Release would grow. Sustained Izanagi would no longer be theoretical.
He did not fear losing control.
There was something colder beneath everything. An emptiness accumulated over a long stretch of memory. When necessary, he could release it, erasing excess emotion as cleanly as cutting thread.
Balance.
Still, all of this remained conjecture.
He had no proof the Box could elevate a three-tomoe Sharingan. No confirmation that his assumptions would hold. The Box itself required a sacrifice. Chakra on a scale few could provide.
In the past, it had been opened using a portion of the Nine-Tails' power.
That alone spoke volumes.
Sasuke rested his hand against his jaw, thinking.
Then his expression shifted.
He straightened, exhaled, and allowed himself a brief, ordinary smile. A habit. A reminder. Solitude dulled him too easily if he allowed it.
The outline of the plan was enough for now.
The Box of Bliss and the third eye were steps further down the path.
What came first was far simpler.
Eternal Mangekyō.
And killing the snake.