Sakura could also be a main character. As a medic - ninja, she might be involved in Naruto's treatment in the mental hospital. She could bring her own knowledge and her relationship with Naruto into play, adding depth to the story.
Obviously, Harry Potter himself could be one of the main characters. Maybe he's been through so much during the fight against Voldemort that he starts to have mental health issues and ends up in the mental hospital. Hermione would also be a likely main character as she would be trying to find a way to cure Harry using her vast knowledge of magic. Another could be Luna Lovegood. Her unique perspective on the world might make her either a patient who is wrongly diagnosed or a healer who has her own unorthodox methods of treating the mentally ill wizards.
Another character could be Kakashi. He might be the one who doubts the decision to send Naruto to the mental hospital. He could secretly visit Naruto and try to train him in mental fortitude techniques so that he can get out of the hospital sooner.
Naruto could also be a main character, even if he's not a medical expert. He could be visiting his injured friends in the hospital and accidentally stumble upon a conspiracy. His determination and never - give - up attitude would be useful in uncovering the truth.
Well, perhaps in this fanfiction, some of Naruto's friends are also in the mental hospital for various reasons. For example, Sasuke might be there because of his inner turmoil and the darkness he has carried. The story could explore how they interact and support each other in this unusual setting, which is quite different from their usual ninja world adventures.
Perhaps a powerful monster in disguise as a doctor or staff member. They could be using the hospital's resources to create a portal to the underworld or something equally dangerous, and Percy has to stop them. They would be constantly trying to drive Percy crazy or keep him from interfering with their plans.
Lucy might also be a suitable main character. Her kind heart would lead her to try and help the other patients. She could use her celestial magic in unique ways to communicate with those who seem lost in their own minds. Maybe she gets trapped in the mental hospital while looking for a lost Celestial Spirit item and has to find a way to escape while also helping those in need.
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.
Obviously, Naruto could be one of the main characters. He could be either a patient or someone helping out at the hospital. Another main character could be Sakura. Since she has medical skills, she could be a doctor or a medic - ninja in charge at the hospital. And then there could be a new character, like a young orphan who is being trained as a medic - ninja at the hospital and has an interesting backstory.
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.
Well, one possible plot could be that Naruto has faced so many traumas during his battles and the loss of his friends that it finally takes a toll on his mental health, leading to him being sent to a mental hospital. In the hospital, he might have to deal with his inner demons, like the Nine - Tails' influence on his psyche, and try to find a way to heal.