If I had to give a reason, it would be that Kagami Uchiha held the Shinobi World Martial Performance.
It was both a spur-of-the-moment decision and a long-planned scheme.
Kagami Uchiha always believed that only in real battles can the strong grow stronger.
Shisui and his clansmen were people he cared about, and so was Minato.
He also hopes to have someone he loves and to have his own children.
But he will not create his own weaknesses until everything is settled, and he will restrain his emotions in this regard.
At least... until all the so-called Ōtsutsuki are wiped out.
He has embarked on a new path and can see the road ahead.
Shisui still has the Three-Tomoe Sharingan, which is the effect of his personal suppression.
Although Shisui had not suffered any major trauma, the Yin Release Chakra he had accumulated was enough for him to awaken the Mangekyo.
Kagami Uchiha studied Uchiha Fugaku Mangekyo and verified his conjecture.
In the Shinobi World, only two pairs of Eternal Mangekyo have ever existed.
The first one is Uchiha Madara, and Sasuke will be next.
They have one thing in common.
He is the reincarnation of Indra's Chakra.
Uchiha Itachi said that Mangekyou Mangekyo with similar bloodlines would combine to form a pair of Eternal Mangekyo, a conclusion he drew from Uchiha Madara.
Prior to this, there was only one case Uchiha Madara, so we cannot draw conclusions based on this alone.
Is it possible that only the Mangekyo of the reincarnation of Indra, by absorbing the power of another pair of Mangekyo, could have perfected its evolution?
Two Mangekyo that are simply related by blood cannot be combined to form Eternal Mangekyo.
Mangekyo is simply an imperfect evolution.
Therefore, Kagami Uchiha never considered himself to have Eternal Mangekyo, but rather Perfect Mangekyo.
The Eternal Mangekyo Rinnegan are evolutionary paths belonging to the reincarnations of Indra, and ordinary Uchiha clan members are not qualified to attain them.
Uchiha Obito, who briefly gained the Six Paths Power, possessed Kamui granted him the ability to traverse between two worlds.
Kakashi, endowed with dual Kamui, was even able to inflict damage on Kekkei Mōra Kaguya.
Kamui is still Kamui.
This is the effect that Kagami Uchiha hoped for.
The Mangekyō Sharingan is a manifestation of the owner's strong desires.
The known abilities of the Rinnegan are indeed powerful, but this particular characteristic is not present.
You can't exactly say that Sasuke's wish is to teleport, can you?
The Rinnegan is the eye of the Ōtsutsuki Clan, and the Sharingan originates from the God Tree.
Combining the two, Kaguya Otsutsuki, who possesses the Rinne Sharingan, can unleash the Infinite Tsukuyomi, which covers the entire planet.
She succeeded once before.
Why did it fail...?
It's because of her two children.
Whether the Sage of Six Paths brothers were born through Kaguya's intervention or through the prayers of others.
One important point is involved in all of them.
The Shinobi World.
The Sage of Sage of Six Paths and his brothers are already considered to be semi-native beings.
Whether it's the world Kagami Uchiha originally existed in, the Jujutsu World, or the Shinobi World.
They all seem to follow a pattern.
Balance.
In the event of a potential world-destroying catastrophe, corresponding life forms will emerge to prevent the disaster.
There is a word that can describe this phenomenon.
It arose in response to the times.
Working backward from the result, the Sage of Sage of Six Paths and his brother were born to prevent Kaguya Otsutsuki from destroying the Shinobi World.
The Jujutsu World.
The birth of Satoru Gojo also seems to be to prevent Sukuna from destroying the world.
That's how it should normally be, but the plot went completely off track there, Sukuna killed Satoru Gojo.
But at least Sukuna is gone too.
In the original timeline, Sasuke and Naruto grew up at the right time and sealed Kaguya.
After that, Boruto might take on that role.
Against this backdrop, coupled with the previously mentioned Mangekyo- like wish-granting mechanism...
Kagami Uchiha speculated...
The world possesses a will.
It is not an existence that can be precisely described, but rather a set of rules that sustain its own existence.
The Warring States Era lasted for a thousand years, yet not a pair of Mangekyo ever came into existence.
The Uchiha Clan has clear records that Uchiha Madara was the first user of the Mangekyo.
Even Indra, the founder of the Uchiha, did not have the Mangekyo.
The world seems to have foreseen another impending crisis of destruction and is trying to take measures to save itself.
It previously chose the Sage of Sage of Six Paths brothers, as well as Gamamaru, who is now the Great Toad Sage.
Now...
It could be Mangekyo.
Neither the Ōtsutsuki nor the God Tree possesses Mangekyo.
Then, working backward from the ending...
Kamui Kaguya's Mangekyo was indeed crucial in sealing her Kaguya!
The dual Kamui are like a replacement for Gamamaru's role in history.
Obito, with his dual Kamui, shielded the Obito from a potentially fatal attack by using the All-Killing Ash Bones.
Kakashi, with his dual Kamui, severely injured Kaguya, creating an opportunity to seal her away.
This speculation arises because Kagami Uchiha attained the Mangekyo while in a calm state.
I've experienced that feeling carefully.
When the time is right, heaven and earth will lend their strength.
That rapid collision of thoughts, the instantaneous understanding of things that were previously incomprehensible.
It's like...
An inexplicable force intervened, following your own desires, and gave you a hard push.
Based on this conjecture, he attached great importance to Shisui's promotion.
The original Shisui struggled between his clan and the village, trying to avoid causing conflict, and thus awakened Kotoamatsukami.
Now that he is not in this predicament, it is unknown whether he can awaken the Kotoamatsukami.
A simple Mangekyo Kotoamatsukami would not be effective against a powerhouse at the Rinnegan level, as the energy levels of their eye powers are worlds apart.
We must guide him onto his own path of Perfect Mangekyo.
Furthermore, he cannot have any anger or vengeful emotions when he awakens the Mangekyo.
Otherwise, if Amaterasu awakens, everything will be over.
After all, Amaterasu, with her Eternal Mangekyo -level power, only has so-so expressiveness and is completely useless against Ōtsutsuki.
Kagami Uchiha still prefers to have Shisui awaken Dōjutsu that amplifies his own abilities, or a support-type Dōjutsu, just like himself.
When your own combat strength is sufficient, auxiliary Dōjutsu are the most useful.
Just like Ōtsutsuki Isshiki's ability to Sukunahikona, when combined with Taijutsu, it becomes ridiculously powerful.
As for Sasuke, Kagami Uchiha wouldn't put in that much effort, since Sasuke already had his own path to advancement.
One Eternal Eyes and one Rinnegan would be good, as long as his physique is improved.
It would be best to arrange for him to awaken a Dōjutsu that enhances his physical constitution.
To this end, Kagami Uchiha had two Uzumaki Clan children Tenten stimulating his physical abilities.
Alas, that's how it is with the Uchiha; their relatively weak bodies cannot withstand the rapidly growing power of their eyes.
There are ways to solve this.
Naruto Uzumaki and Hinata Hyuga's child inherited their physique and eyes.
What about the descendants of the Uchiha and Uzumaki?
Uchiha Mikoto has no right to decide not to cook for Sasuke.
It was Kagami Uchiha who was trying to bring Sasuke and Karin together.
Gazing at the seemingly endless rift valley, Kagami Uchiha dispelled his Susanoo.
He flew towards Konoha, intending to gather everyone and announce his decision.