There could be some new characters created specifically for the fanfic. Maybe a mysterious wizard who mentors Sakura's sister, or a group of outcasts that she befriends. And of course, there might be antagonists such as an envious classmate or a dark magic user who wants to cause trouble for the sisters.
Obviously, Sakura's sister would be a main character. Sakura herself might also be in it, as well as their friends. There could be a cute animal sidekick too, like a talking cat or a little fairy.
There could be original characters created specifically for this fanfic. These new characters might be the source of Sakura's anger. For instance, a new villain who has targeted Sakura or her loved ones. Or it could be a rival who constantly undermines Sakura, causing her to be angry. Additionally, characters from other related series might make cameo appearances if it's a crossover - type fanfic.
Obviously, Sakura herself is the main character. Naruto could also be in it. Maybe he tries to convince Sakura to stay or he could be the one to help her prepare for her journey. Sasuke might be another character. He could have some influence on Sakura's decision to leave, either by his own actions or just his presence in the village.
Obviously, Sakura's mother herself. And her family members like her parents or siblings if they are relevant to the story. They could have influenced her in different ways.
There could be the narrator, who is the one trying to get away from Sakura. Maybe there's also a best friend of the narrator who encourages them to break free from Sakura. For instance, this friend might see the negative impact Sakura has on the narrator's life and gives advice on how to get away.
There could also be an antagonist, perhaps the abuser. This character would play a crucial role in driving the conflict in the story. They could be a complex character with their own motives, though their actions are clearly wrong.
Well, obviously Sakura's sister would be a main character. And Sakura herself often plays a significant role as well. Sometimes other characters from the original series like Naruto or Sasuke might make appearances, especially if the story is set in the same universe and their actions impact the sisters in some way.
The obvious main character could be the one who ends up in Sakura's body. It could be an original character created by the fanfiction writer.
I'm not entirely sure if there are a large number of them, but it's not uncommon for fanfic writers to come up with these sorts of unexpected character connections. In the Naruto universe, Sakura and Sasori are from different groups, but in a fanfic, the idea of them being siblings can lead to all kinds of interesting plot developments, like how it might change their interactions with other characters or their own personal growth within the story.
Obviously, Sakura is one of the main characters. She is a strong and determined kunoichi. And then there's Sasori's sister. We don't know much about her yet, but she's likely to be a complex character, perhaps influenced by Sasori's actions and reputation in the ninja world.
There could be the prison guards. Some might be cruel and strict, while others could be more sympathetic. Also, other inmates. Maybe an older, experienced inmate who becomes a mentor - like figure to Sakura.