In fanfiction, when Naruto goes to the hospital, he could discover a new medical jutsu being developed there. He might get involved in the process, either by accident or because the doctors need his help. Since he has so much chakra, it could be useful for testing or something related to the new jutsu.
Maybe Harry is injured during a Quidditch match and has to be rushed to the hospital. There he might meet some interesting new characters, like a healer with a mysterious past.
In the fanfiction, Danny might be in the hospital because of his ghost - fighting injuries. Maybe he has to hide his ghost powers from the doctors while trying to recover.
In this fanfiction, maybe the Pokemon gets injured during its trip and has to be treated in the hospital. For example, it could have been in a battle with a wild Pokemon and got hurt.
There might also be some hospital staff Pokemon, like Chansey, which is known for being a nurse in the Pokemon world. They could play important roles in the fanfiction, helping the sick or injured Pokemon and interacting with the trainer and the Pokemon on the trip.
Perhaps Harry will run into an old wizard who has been in the hospital for a long time. This wizard has a lot of stories about the old days of the wizarding world and gives Harry some valuable advice.
He might meet a nurse who has some sort of psychic ability and can sense that Danny is different. This could lead to an interesting interaction where Danny has to be extra careful.
Well, in some fanfiction, Naruto could be in the hospital because of a new and strange illness that no one has seen before. The story could focus on the doctors in the ninja world trying to figure out a cure. And Naruto being Naruto, he might be cracking jokes with the nurses and other patients, spreading his positive energy even while sick.
It's possible that there's a strange illness going around the village and Naruto goes to the hospital to see if he can offer any help. He has a strong sense of justice and would want to do whatever he can to stop the spread of the illness and make sure everyone gets better.