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.
Besides Sakura, there could be a prison doctor. This character could play an important role, perhaps being involved in some unethical experiments or being the only one who believes in Sakura's innocence. There might also be a group of rebel inmates who are planning a revolt against the prison system. They could initially be skeptical of Sakura but later accept her as one of their own. And of course, there could be informants within the prison, inmates who work for the guards in exchange for certain privileges.
In this fanfiction, there might be a warden who is the main authority figure in Owa prison. He or she could be corrupt or fair, depending on the direction of the story. There may also be other prisoners who have their own vendettas or goals. For example, a prisoner who has been in the prison for a long time and has a lot of influence among the inmates. Additionally, there could be visitors to the prison, like Sakura's friends or family members who try to help her in some way.
The plot of 'sakura was at owa prison fanfiction' could involve Sakura being sent to Owa prison as a punishment for a crime she may or may not have committed. Once there, she discovers a hidden underworld within the prison. There could be secret groups, power struggles, and she might find herself in the middle of it all. She may use her unique skills, whether they are combat - related or her wits, to survive and maybe even expose the dark secrets of the prison.
The Akatsuki members would be the main ones. It could include Itachi, who is known for his complex character and powerful abilities. His relationship with Sakura could be an interesting aspect, whether it's one of mutual respect or a more adversarial one.
Sasuke is also frequently present. His complex relationship with Sakura can be further explored in the fanfiction. The reincarnated character could either get involved in their relationship or try to change the dynamics between them.
There could be the patients, of course. Each patient might have their own unique backstory and personality. Maybe there's a young patient who is dealing with trauma, and Sakura has to find a way to reach out to them.
Sakura's friends like Naruto and Sasuke could be main characters. They might be the ones trying to find a way to save her. They could be using their skills and powers to look for a cure or a solution.
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.
One of the main characters could be Sakura's mother. Mothers are often intuitive about their children's problems. She could be the one who eventually helps Sakura open up about her self - harm. Then, there might be a new acquaintance in Sakura's life, someone she meets randomly. This person could have had a similar experience in the past and be able to offer unique advice and support to Sakura.
Tomoyo would also be an important character. She would be very worried about Sakura. She might use her skills in making costumes to create some special baby clothes for Sakura. And she would be constantly by Sakura's side, taking care of her and trying to comfort her.
Maybe there's a mentor figure in Sakura's life. After Sakura makes a mistake, the mentor could guide her on how to make a proper apology and help her understand the importance of taking responsibility for her actions. This character could add depth to the story by providing wisdom and advice.
Definitely some of the Akatsuki members. Itachi could be one. He is a complex character with his own motives. His presence could add a lot of mystery to the story as Sakura might try to figure out his true intentions. Another could be Deidara. His explosive personality and love for destruction could create some intense confrontations with Sakura.