The sun had just begun to warm the leaves of the forest. Shisui and Itachi sat facing each other, observing the ground covered in branches and moss.
"Before you perform any physical jutsu," Shisui began, "you must understand something: genjutsu isn't about brute force. It's not about manipulating chakra like a blunt weapon. It's about perception. It's about deceiving the enemy's senses."
Itachi frowned, crossing his arms.
Perception… hmm. Like manipulating sensory information, like a computer program…
"How does it work, exactly?" he finally asked.
Shisui smiled, amused.
"Think of the mind as a system of circuits. Every perception is a piece of data. If you can alter the interpretation of that data, you can make someone see whatever you want."
Itachi nodded slowly, absorbing every word.
"So, if I understand the patterns and propagation of chakra that affect the sensory nerves… I could model illusions in a controlled manner."
Shisui raised an eyebrow.
"Interesting. But remember, this isn't just theory. Practice requires timing, precision, and absolute control of your chakra."
The first exercise was simple: concentrate chakra at a fixed point in front of him and slightly alter Shisui's perception.
Itachi visualized waves of energy, thinking of them as electrical impulses that could trick vision. He concentrated his chakra, and suddenly Shisui blinked.
"Interesting," he said. "You've altered my perception, albeit minimally."
Itachi mentally noted every detail: intensity, reaction time, duration of the illusion. For him, this was pure experimentation: variables, hypotheses, tests, measurements.
"Now try to manipulate an object," said Shisui. "Make it seem like it's moving or disappearing."
Itachi took a small stone and concentrated his chakra around it, trying to "reprogram" Shisui's perception. The stone didn't move physically, but Shisui blinked and reached out to where he thought it was.
"It works," whispered Itachi, fascinated. "Illusions are manipulations of sensory information, controlled by chakra flow."
For hours, the exercises continued. Shisui taught the principles of Genjutsu:
How to manipulate specific perceptual channels. How to create partial illusions first, then combine them into complex patterns. How to measure the target's reaction time.
Itachi took mental notes of everything, comparing it to his past experience in physics:
If this is sensory information, I could quantify it, alter it, and predict outcomes… like a laboratory experiment.
At the end of the day, both sat on the grass, tired but exhilarated.
"You have talent," said Shisui. "Not just for chakra control, but for how you think."
Itachi smiled, but his mind was already racing:
I can map the perceptual channels, measure the intensity of illusions, even attempt to create a genjutsu that functions like an experiment… without relying on brute force.
The forest was silent, and for the first time, Itachi felt he had someone with whom to share his theories and experiments—someone who would push him to explore the frontier between science and the shinobi arts.
The forest was quiet at dawn. Itachi was concentrated by a small stream, with several leaves and branches aligned around him. He had decided on an ambitious experiment: to test his chakra's elemental affinity and, at the same time, advance his control of the Rasengan, which until now he could only form partially and for brief seconds.
He concentrated chakra in his palm, creating a mini Rasengan. This time, he didn't do it randomly: he modulated the rotation, compression, and stability as if they were variables in a lab. The sphere appeared, spinning with a faint hum. It seemed perfect… and then, it vanished.
Itachi frowned and decided to apply a principle he remembered from Shisui: genjutsu. He didn't think of it as an illusion on someone else, but as a self-genjutsu, a small deception directed at himself. He concentrated chakra, subtly altering the perception of his own senses: he made his mind believe the Rasengan was already working perfectly.
And then something unexpected happened. The illusion didn't just deceive his perception; his brain and chakra aligned as never before, unlocking a real control he hadn't been able to sustain. The sphere stabilized in his palm, spinning perfectly without disintegrating.
Itachi opened his eyes and saw the flows of chakra in the stream, in the leaves, even in the wind moving through the trees. The emotion was so intense that his heart raced and a warmth spread through his vision: his Sharingan awakened.
There was no pain, no fear. Only absolute clarity: he could see the chakra flows and energy channels as if they were lines of force in a physics experiment. The combination of discovery, control, and wonder had activated his ocular power.
After stabilizing the mini Rasengan, Itachi began the affinity tests:
A leaf wrinkled upon contact with his chakra → Fire affinity. Another split with a light touch of wind → Incipient Wind affinity. The water in the stream vibrated slightly when touched → Potential Lightning affinity.
Itachi mentally recorded the results: he had multiple possible attributes, though fire remained dominant. This information would be key to training his jutsus with precision and developing more complex combinations.
Shisui appeared silently, watching attentively.
"I see something has changed," he said. "You have control… and something more."
Itachi smiled with a mix of satisfaction and scientific curiosity.
"Not just control… I can see how it all works. And I've achieved something I once thought impossible: my Rasengan works completely now."
Shisui nodded, intrigued.
"You achieved it with your own hands… and with a genjutsu applied to yourself. Interesting. I've never seen an awakening so tied to discovery and intellectual emotion."
Itachi understood that his world had changed: he could now experiment without limits, combining the Rasengan, genjutsu, and chakra control. Every leaf, every current of water, every flow of energy would be a miniature laboratory.