So this is more of a what if... You could use original Shisui or have the MC be reborn as Shisui
Scenario: What if during the nine tails attack, Shisui (Age 7) decided to help against the nine tails after finding out that an Uchiha could control it with their sharingan (Shisui had his mangekyo at age 7) What if he managed to take over control of the Kyuubi to allow Minato to seal the nine tails in Naruto. What if Minato and Kushina survived that night, What would happen to the Uchiha Clan and how much would this one change, change the story.
I got this idea after thinking about what if they allowed the Uchiha to help during the attack, I used shisui because he could have been one of the most powerful Ninja ever if it wasn't for Danzo