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.
In the 'naruto sent to a mental hospital fanfiction', it could start with Naruto overusing his chakra in a fight and having some sort of mental breakdown as a result. The village elders, not fully understanding what's going on, decide to send him to a mental hospital for treatment. Inside, Naruto discovers that there are other ninjas there too, some of whom have lost their powers in strange ways. He then tries to find a way to regain his strength and sanity while also helping his new friends.
Maybe in this fanfiction, Naruto is wrongly accused of something he didn't do, like a supposed act of aggression during a mission. This false accusation and the pressure from the village make him seem 'crazy' to others, so they send him to a mental hospital. There, he meets other patients with different backstories, and they all help each other in unexpected ways.
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.
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.
Perhaps Sakura is in the mental hospital because she was wrongly committed. In the fanfiction, she could be trying to prove her sanity. Along the way, she forms unexpected friendships with other patients and staff members. These relationships help her on her journey to regain her freedom and also help her come to terms with parts of herself she didn't understand before.
One possible plot could be that some of the Hogwarts students end up in a mental hospital due to the trauma of the wizarding wars. They form a support group within the hospital, using magic secretly to heal each other's mental scars. For example, Harry Potter could be haunted by the deaths he witnessed and struggle with PTSD in the hospital. Hermione might use her knowledge to research magical cures for mental illness.
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.
Perhaps in the fanfiction, Sakura Haruno discovers some secrets within the mental hospital. It could be about a hidden experiment or a patient with a very special ability that she has to handle while also trying to keep the hospital running smoothly.
One possible plot could be Sakura's journey in understanding the patients at Iruka Mental Hospital. She might start as a novice, making mistakes but gradually learning to empathize. For example, she could encounter a patient who has a unique form of amnesia. Sakura tries different therapeutic methods she has learned to help the patient recall memories. Through this process, she not only helps the patient but also grows as a professional.
In a 'Naruto sent to hell' fanfiction, it could be that Naruto is sent to hell as part of a test. The gods or some powerful entities want to see if he can bring hope and change to the damned souls in hell. So, Naruto starts to teach the souls in hell about friendship, perseverance and the ninja way. He tries to reform the place from within, facing many challenges along the way like powerful hell guards and the dark energy that tries to corrupt him.
One possible plot could be that Percy wakes up in the mental hospital with no memory of how he got there. He starts to notice strange things like the nurses and doctors seem to have an otherworldly aura. As he tries to regain his memory, he discovers that the hospital is a front for some sort of mythological experiment. He then teams up with other demigods who are also trapped there to escape and expose the truth.
Well, he might meet other characters who also claim to have had strange experiences. They could form a sort of alliance, thinking they are all in the same boat, not realizing Percy's experiences are real in the context of the Percy Jackson universe. They could plan an escape together, believing they are being wrongly held.