It could be a rogue ninja who has a vendetta against the Uchiha clan. Since Itachi and Sarada are both Uchihas, this antagonist might target them. Maybe he wants to steal the secrets of the Sharingan from them.
Perhaps the main antagonist could be a powerful figure from another village who sees the combination of Itachi's skills and Sarada's potential as a threat. They might try to eliminate them to prevent the Uchiha clan from becoming too powerful again. This could lead to a lot of action - packed battles in the fanfiction.
Itachi would probably be very calm and composed. He might see Sarada as a symbol of the new generation of ninjas in the village. He could be gentle with her, perhaps sensing her potential and her desire to grow as a ninja.
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.
At first, it could be a bit awkward. Sarada has only heard stories about Itachi. But as they start to interact, they might develop a mentor - mentee relationship. Itachi could see Sarada's potential and start to guide her.
Itachi in this type of fanfiction usually maintains his mysterious aura. He doesn't reveal everything at once, which makes Sarada even more curious. He is still the self - sacrificing character we know from the original series. Sarada is depicted as a strong - willed girl. She respects Itachi greatly and is quick to pick up on the lessons he imparts. She also has her own ideas and isn't afraid to voice them out, which sometimes challenges Itachi's traditional ways of thinking.
Itachi's skills and wisdom would no doubt rub off on Sarada. His combat expertise and his way of thinking could give Sarada new ideas on how to approach battles and solve problems. This would make her a more well - rounded and formidable ninja, thus contributing to her growth in the ninja world.
Madara Uchiha could still be a great antagonist. Even with Itachi and Naruto teaming up, Madara's power and his long - term plans for the ninja world would pose a huge threat. His knowledge of the Sharingan and his connection to the Uchiha clan would make for an interesting conflict against Itachi, while his overall strength would be a challenge for Naruto as well.
It could be Orochimaru. He has always been interested in obtaining powerful jutsu and the Sharingan. If he catches wind of Itachi teaching Naruto, he might see Naruto as a new target to either steal power from or use as a pawn against Itachi and the Leaf Village.
Well, perhaps Sarada could be initially in awe of Itachi. She might learn some unique jutsu techniques from him in the fanfiction. It could also be a scenario where Itachi gives her some sage advice on how to handle her own powers and responsibilities within the Uchiha clan.
A possible relationship could be one of mutual respect. Sarada would respect Itachi for his skills and his past sacrifices. Itachi, on the other hand, might see Sarada as a symbol of hope for the future of the Uchiha clan. They could share stories about the Uchiha, with Itachi passing on the history and traditions that Sarada might not be fully aware of. This could strengthen their bond and lead to a deeper understanding between them. In the fanfiction, they might also team up to face a common enemy, relying on each other's strengths and abilities, which would further solidify their relationship.
One possibility is that Sarada, being an Uchiha herself, would be in awe of Itachi. She might ask him about the secrets of the Sharingan, as Itachi was a master of it. Itachi could see the potential in Sarada and offer her some wisdom about the Uchiha legacy and how to handle the power of the Sharingan responsibly.