In a fanfiction where Shisui meets baby Sarada, Shisui might be feeling a bit melancholic as he has seen so much turmoil in the village. But when he sees Sarada, he feels a glimmer of hope. He may hold her gently and think about how she is the future of the Uchiha clan. He could even vow silently to protect her from the shadows, just as he has always tried to protect the village.
In this fanfiction, Shisui could be a mentor figure to baby Sarada in a way. He might not be able to be there all the time, but when he is around, he imparts some of his wisdom. He could teach her (in a very basic sense for a baby) about the importance of loyalty and courage. He may also give her a special gift that has some connection to his own powers, like a pendant that can enhance her chakra control when she grows up, starting her on a path of becoming a strong ninja.
Well, it could be about Itachi being in a situation where he encounters baby Sarada by chance. Maybe he has some sort of premonition about her future importance in the ninja world. He might be gentle with her, showing a side of him that's rarely seen, perhaps sharing a moment of calmness in the midst of the chaos that usually surrounds him.
There could be Sasuke. Since Sarada is his daughter, he might be in the background, either not aware of the encounter yet or on his way to find Sarada. Naruto could also be a character. He has a connection to both Itachi and Sasuke, and he might play a role in the events that lead up to or follow the encounter. Another possible character could be Sakura. As Sarada's mother, she would be worried if Sarada was out of her sight and her actions to find Sarada could be part of the story.
One possible scenario in this fanfiction could be Fugaku seeing Sarada's potential and taking her under his wing to train her. He might recognize her Uchiha blood and want to ensure she becomes a strong shinobi like the Uchiha of old.
Shisui, on the other hand, would probably be more open and friendly towards Sarada right away. He could share some of his own experiences with her, especially about loyalty and friendship. Maybe he would teach her some of his unique jutsu techniques in a friendly sparring session. Sarada would surely be in awe of these two legendary shinobi and learn a great deal from them, which could shape her future actions and decisions in the fanfiction.
In a Sarada meets past Sasuke fanfiction, it could be that Sarada has to keep her identity a secret at first. She might be on a mission in the past for some reason. As she observes past Sasuke, she could notice his skills and the way he interacts with others, like Naruto. This would give her a chance to understand the bond between her father and Naruto from a whole new perspective, which could be really interesting for the readers.
In the fanfiction, the interaction between Sarada and Sasuke's family could be filled with emotions. Maybe Sasuke's family has high expectations of Sarada, given her relation to Sasuke. This could create some tension at first, but as they get to know her better, they start to accept and love her.