Well, Naruto would be a likely character. He and Sakura are friends, and he'd probably be really worried about her. He might visit often and try to cheer her up with his goofy antics. Another could be Sasuke. Even if he's a bit more aloof, his presence would add an interesting dynamic. He could come to see her out of his own sense of obligation or perhaps a deeper, unspoken feeling.
Ino could be a major character. Since she and Sakura have a complex relationship that has evolved over time. Ino might be there to offer both support and a bit of friendly rivalry. She could bring flowers to Sakura's bedside and they could have some heartfelt conversations about their past and future as kunoichi. Also, Kakashi could be there as Sakura's mentor. He would offer wisdom and guidance during her hospital stay, perhaps sharing some of his own experiences with injury and recovery.
Tsunade could be a significant character. As the Hokage and a medical expert like Sakura, she could have some knowledge about the crystal. She might offer advice or warnings to Sakura. Then there's Shizune, who could assist Tsunade in dealing with Sakura and the crystal situation. And of course, Orochimaru might be a potential villain, interested in the crystal's power for his own dark experiments.
There could be some original characters created specifically for this fanfiction. Maybe a mysterious mentor figure who claims to be able to help Sakura control her dark side, but has their own ulterior motives. Also, her sensei Kakashi could be there, trying to figure out how to guide Sakura through this difficult time.
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.
One character could be Naruto. He might be Sakura's friend, but completely oblivious to her hidden pain. He's so focused on his own goals that he doesn't notice Sakura's struggle, which could add to her feelings of loneliness.
It could be Naruto. Since he has always been a big part of Sakura's life, he might be one of the main characters trying to figure out what's wrong with Sakura and how to bring back the old her.
Naruto could be a great addition. His friendship with Sakura and his complex relationship with Kabuto in the original series could add an interesting dynamic. For example, Naruto might suspect something is going on between Sakura and Kabuto and try to interfere or understand what's happening.
It could be an old and wise hermit who lives in the forest. This hermit has seen many things and has a vast knowledge of the skills sakura wants to learn. He guides her with tough love, pushing her to her limits but also providing valuable advice when she's in doubt.
It could be a rival ninja clan if this is in a ninja - themed story. They might see Sakura as a valuable asset to get information about her own clan or to use her skills against her people.
The hospital staff also feature prominently. Nurses and doctors play important roles. A strict but kind - hearted doctor could be a main character, who is dedicated to finding new ways to treat the patients in Sakura Mental Hospital. The fanfiction might show their daily struggles and triumphs in dealing with the patients.
Well, in addition to Sakura, there might be a strict but fair psychiatrist. He could be a key character as he tries to diagnose and treat Sakura. There could also be a group of patients that Sakura befriends. For instance, a young girl who is in the hospital due to severe anxiety and an older man who has hallucinations. These characters could interact with Sakura in different ways, some being helpful, others being a hindrance to her progress in the mental hospital.