Well, generally in 'sakura meets the uchihas fanfiction', it could be that Sakura meets the Uchihas in a post - war scenario. She might be trying to help the remaining Uchihas rebuild or she could be on a mission to understand more about their Sharingan powers. There could also be a romantic sub - plot where Sakura falls in love with an Uchiha character, but that depends on the writer's intention.
I'm not sure specifically as there could be many different plots in such a fanfiction. It might involve Sakura having various interactions with the Uchiha clan members, perhaps she forms new friendships, or gets involved in some adventures related to the Uchiha's unique abilities and their history.
The main character is Sakura. For the Uchiha side, Sasuke is a no - brainer as a main character in this fanfiction. But it could also include some other Uchiha characters that are not as prominent in the original series. For instance, a young Uchiha who is just starting to discover their Sharingan powers and Sakura becomes a mentor - like figure to them. Or perhaps an older Uchiha who has survived some great tragedy and Sakura helps them come to terms with their past, all while exploring the unique culture and abilities of the Uchiha clan.
In a 'sakura brother killed the uchihas' fanfiction, the plot could start with the Sakura brother having a hidden power or ability that the Uchihas unknowingly pose a threat to. He might see the Uchihas as a danger to his sister or to the village in general. And as a result, he decides to take matters into his own hands and eliminate them. Or it could be that he is misinformed about the Uchihas and thinks they are evil, leading to his actions.
One possible plot could be that future Sakura, with her advanced medical skills and battle experience, goes back in time and meets a younger Sasuke. She might try to prevent some of the tragedies that Sasuke later endures. For example, she could warn him about Orochimaru's true intentions, which would change the course of Sasuke's journey. This would also lead to different interactions between Sakura and Sasuke compared to the original story. Their relationship might develop in a more positive way earlier on, as Sakura from the future has a deeper understanding of Sasuke's pain and the consequences of his actions.
A different plot could be that Sasuke meets Sakura at a medical convention in another village. Sakura is there to present some of her latest medical ninja research. Sasuke is initially there for other reasons but seeing Sakura makes him realize how much he has missed her and their connection.
One possible plot could be that Tobi, Sakura, and the female reader all end up on a mission together. Tobi's unpredictable nature might create some comical situations at first. Sakura, with her medical and combat skills, would be a reliable ally. And the female reader could have some unique abilities that help them overcome the challenges in the mission, like perhaps the ability to communicate with animals which gives them an edge in a forest - type mission.
One possible plot could be that Sakura somehow travels back in time and meets Kushina. Kushina, being Naruto's mother, could see some of Naruto in Sakura and they could bond over that. Maybe Kushina would teach Sakura some of her unique ninja techniques or give her advice on how to deal with difficult situations in the ninja world.
I haven't come across a 'sakura brother killed the uchihas' fanfiction. It could be a really unique and perhaps not very mainstream idea. Fanfiction often has a wide range of themes, but this seems rather unusual. Maybe it's a very specific creation within a small group of fans.
In Akatsuki fanfiction, one of the possible female Uchihas could be an original character created by the author. For example, she might be a long - lost relative of the main Uchiha clan members. She could possess unique Sharingan abilities that set her apart from the male Uchihas in the story.
One common theme is redemption. Since Obito has done a lot of bad things, in many fanfictions Sakura becomes a catalyst for his redemption. For example, she might show him the good in the world again.
One common theme is the discovery of self. When Sakura meets Kurama, both characters often start to learn more about themselves. For example, Sakura might find new aspects of her strength, and Kurama might re - evaluate his view of humans.