Shisui Being alive changes every single incident possible(like for instance Kaguya being alive but not attacking, BZ being happily rejoined with his mother, itachi not having to kill uchiha clan, Obito never going astray,Madara using rinne rebirth to let dead ones being alive and Momoshiki and other okutsuki working for kaguya and so on) This will change the complete Naruto story and it will become personal story of ninja who single handedly changed everything..... Uchiha Shisui....

I'm still confuse though 'bout Shisui's MS capabilities and limit. I have mentioned about the Kotoamatsukami and the entering the mind and stuff like that and being it a powerful Genjutsu. But what confuses me is why Danzo, who of course implanted the eye to himself, didn't use it against the Third or the Fifth Hokage to have them on his side. Or he already did but it didn't work.

So I'm questioning if the Kotoamatsukami has a limit on whoever it effects.

well what you are questioning is Danzo's moral and ethics, and I am pretty sure he owed his debt to hiruzen for letting him off hook for trying to assassinate him(via kakashi) if he tried any such thing suspicion would rise on him.(since he can't use it on every single jonin during the vote for hokage). Or maybe he was some kind of complicated arrogant who didn't use his eyes.

Ah, I see.

As shown in the Gokage summit, it's fairly easy to detect. Especially in a village with Sharingan and Byakugan, it would be really hard to hide such a jutsu in such an influential person.

But Danzo had the well-being of the village in mind. He wanted to become Hokage when the time needed him, but he was also aware that he was able to do far more from the shadows. So it's unlikely he would just Koto his lifelog friend to get what he wants, especially since he can't use the jutsu very often and is better off using it to defend Konoha.

Ao didn't detect kotoamatsukami... He just sensed shisui's chakra. And asked for explanation. Noone can detect Koto unless by hunch he guesses that could he be in genjutsu?(something what Ao did, Even with sharingan too one won't be able to guess it for the very same reason).

No yeah, if Shisui was there, he could use his super genjutsu (i forgot what its called) on obito and madara. So no kaguya, loss of life, ten tails rebirth.....so yeah. Only problem is kabuto, but shisui can just tag team him with sasuke (itachi would still be controlled) and izanami him (as ms isn't required for that)