Uchiha Shisui rose rapidly after the Third Great Ninja War, his name "Shunshin Shisui" shaking the Ninja World.
In the original work, Shisui never truly demonstrated his strength; his power was mostly conveyed through the words of others.
For example, Ao of the Hidden Mist Village once said, "Uchiha Shisui's Dojutsu enters the opponent's mind to manipulate them, forcing the opponent to experience reality through his will. For the manipulated person to be completely unaware is the highest-level Dojutsu!"
Killer Bee, the Eight-Tails Jinchuriki, also said that Uchiha Shisui was the strongest Genjutsu Ninja in the Uchiha Clan.
There are many similar evaluations.
In Uchiha En's memory, Uchiha Shisui became a Genin in Year 46 of Konoha. In Year 47 of Konoha, he killed his best friend and awakened the Mangekyo. In Year 48 of Konoha, Uchiha Itachi and Uchiha Shisui met, and the Nine-Tailed Fox Attack broke out that same year. (P.S.: These are the details from Itachi Shinden and Itachi's novel.)
Because the Nine-Tailed was controlled by the Sharingan, and the Uchiha Clan was prevented by Danzo from intervening to stop the Nine-Tailed, the Uchiha Clan's position in Konoha became extremely awkward.
Against this backdrop, Uchiha Shisui joined the Anbu.
The personalities within the Uchiha Clan are incredibly diverse: Uchiha Madara's arrogance, Uchiha Obito's early sunny disposition and later ruthlessness, Uchiha Itachi's gloominess, and Uchiha Sasuke's volatility.
Uchiha Shisui was different from these other members of the Uchiha Clan; he was like Obito before Rin Nohara's death—cheerful and always wearing a smile.
With this personality and strength, had he not been born into the Uchiha Clan, he might have been loved by many people, just like the Fourth Hokage, Minato Namikaze.
But unfortunately, Shisui's surname was Uchiha.
In Uchiha En's view, Uchiha Shisui and Uchiha Itachi were still quite different.
Uchiha Itachi was a pure executioner brainwashed by the Will of Fire; it wouldn't be an exaggeration to call him insane. What normal person would turn their blade against their own clan and wipe them out?
Uchiha Shisui was different. Between the Village and the Clan, he didn't blindly favor one side. His greatest wish was to maintain harmony between the Village and the Clan, not to destroy the Clan for the sake of the Village.
To put it plainly, Shisui wasn't entirely on Konoha's side; he just wanted to do his best to prevent bloodshed.
This can be seen from Uchiha Shisui's immediate counterattack when Danzo made his move against him, as well as Uchiha Shisui's uncompromising attitude toward Danzo.
Uchiha Shisui's ideology leaned towards the Clan and the Village being a single entity, prospering together and suffering together.
He didn't want the two sides to become hostile, so he could only mediate between them as much as possible.
Although Shisui's fundamental idea wasn't wrong, he overlooked a key point: the current Village high command did not want the Uchiha Clan to continue existing. Through their various schemes, the conflict between the Village and the Uchiha Clan had reached an irreconcilable point.
Even if Uchiha Shisui had truly used Kotoamatsukami later to stop his clansmen and prevent the Uchiha Clan from rebelling, the Uchiha Clan would still have been wiped out.
And Shisui's fate would have been nothing but death.
Because the moment Shisui revealed the power of Kotoamatsukami, his death was already sealed.
When facing someone who could control your thoughts at any time, anyone would feel fear, let alone the power holders of Konoha like the Third Hokage.
They would certainly worry: what if Uchiha Shisui decided to turn his attention toward the Konoha high command one day?
If Uchiha Shisui's ideology changed even slightly, he could potentially seize control of the entire Konoha and turn the Village into his own puppet.
The system of the Ninja Village dictates that by controlling its high command, one can control the entire Village. Obito controlled the entire Hidden Mist Village by controlling the Fourth Mizukage.
It wasn't just that the Konoha high command didn't trust Shisui; the crucial point was that some among the high command wanted to obtain his power.
In the original work, Danzo once said to Shisui, "You possess the strongest Genjutsu, yet you intend to use such precious power merely to stop a coup d'état?"
Therefore, Shisui's ideas and actions absolutely could not save the Uchiha Clan.
As a Transmigrator, knowing that Shisui's ideology and path were flawed, would it be appropriate to let him continue growing this way?
Of course not!
Uchiha En looked at the Little Shota in front of him and made up his mind: he had to guide Shisui back onto the right path.
The prerequisite for guiding Shisui back onto the right path was definitely establishing a good relationship with him first.
Thinking of this, Uchiha En asked with a kind smile, "Shisui, how old are you this year?"
"I'm 6 years old this year, and I'm a second-year student at the Ninja Academy."
"Six years old, so Shisui is four years younger than me, and three years younger than Obito and Kakashi?" Uchiha En thought to himself.
"Then, Shisui, have you refined your Chakra?" Uchiha En continued to ask.
"Of course! I refined my Chakra when I was in the first year, and I was the first person in our class to refine Chakra!" Uchiha Shisui replied proudly.
"I see! Alright then! I'll teach you the Body Flicker Technique, but learning the Body Flicker Technique requires two prerequisites: strong control over your own Chakra, and quick reflexes."
"Since you are a second-year Ninja Academy student, your control over Chakra is definitely insufficient. If you want to learn the Body Flicker Technique, you should first improve your Chakra control!"
"Senior, how do I improve my Chakra control?" Uchiha Shisui asked.
"Well! You must start with Tree Climbing and Water Walking. Tree Climbing and Water Walking are..." Uchiha En explained the two training methods, Tree Climbing and Water Walking, to Shisui.
However, he did not demonstrate them for Uchiha Shisui.
Uchiha En himself had only just mastered Tree Climbing and Water Walking and wasn't very proficient yet. He was afraid that if something went wrong during the demonstration and he failed, it would be embarrassing.
"Tree Climbing and Water Walking? I understand, Senior, I will definitely practice hard."
"Mhm. One week from now, at this same training ground, I will come to check your progress. If you can master Tree Climbing and Water Walking, I will teach you the next steps."
"Okay, thank you, Senior!"
"You're welcome. We are both members of the Uchiha Clan and should help each other. Oh, by the way, my name is Uchiha En." After saying this, Uchiha En ruffled Shisui's hair and turned to leave.
Watching Uchiha En's retreating figure, Uchiha Shisui muttered to himself, "What a gentle Senior. He's completely different from Senior Tekka!"
Uchiha Tekka is the same age as Obito, both 9 years old, but he did not attend the Ninja Academy in the same year as Uchiha En and Uchiha Obito; he went in the following class.