In this fanfiction, Deku's character development could be quite complex. Going back in time, he may initially be overconfident because he thinks he knows what's going to happen. But as he realizes that changing the past has unforeseen consequences, he becomes more cautious. He also might develop a deeper understanding of his friends and their potential, as he gets to see them at an earlier stage. He could start mentoring some of them, which would in turn make him more responsible and mature as a character.
In the 'Harry goes to the hospital fanfic', it's possible that Harry is injured during a Quidditch match. He is then rushed to the hospital. There, he could discover a hidden part of the hospital that has some ancient magic stored. He might also have some deep conversations with his friends who come to visit him about their future plans and the current state of the wizarding world.
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.
Maybe in the 'manga deku goes back in time fanfiction', Deku goes back to the time before he got his quirk. He then tries to understand the origin of quirks better, using his knowledge from the future. This could lead to him developing his quirk in a completely different way, perhaps even a more powerful way. He might also use this time - travel opportunity to befriend some characters who he didn't have a chance to in the original timeline.
In 'Deku Goes Berserk' fanfiction, a great plot point might be how the other characters react to Deku's new, wild side. For example, Bakugo could initially see it as a sign of weakness, but later realize it's a powerful force that needs to be harnessed. This could lead to a whole new dynamic between them. Another aspect could be how Deku's transformation affects his relationship with All Might. All Might might worry that he's losing control and try to help him in a different way than before.
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.
Perhaps he'll meet an old patient who has been in the hospital for a long time. This patient could tell Harry some long - forgotten stories about Hogwarts in the past. There could also be a chance that he meets some other students who are also in the hospital for various reasons, and they might form a new friendship or alliance.
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.
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.