One possible plotline could be that Hermione breaks her leg during a Quidditch match while she's trying to catch the Snitch. Her friends then have to take care of her and help her keep up with her studies. Another could be that she breaks it while exploring a dangerous part of the Forbidden Forest and they have to figure out how to get her safely back to the castle.
Well, Ron and Harry would most likely be main characters. They're Hermione's best friends, so they'd be right there by her side when she breaks her leg. They'd probably be the ones helping her get to the hospital wing, getting her books for her when she can't walk to the library, and generally just being there for her.
The antagonist could be a cursed object. This object, which has some dark magic in it, might be found by Harry. And when he interacts with it, it starts to control his actions, leading to him breaking Ron's leg. So, in this case, the cursed object is the source of the trouble and can be considered as the antagonist in the fanfiction.
Well, perhaps it could be an accident during a Quidditch match. Harry might accidentally hit Ron with his broomstick while chasing the Snitch, causing Ron's leg to break. It could also be due to a spell gone wrong in a chaotic situation at Hogwarts, like when they're being chased by some dark creatures and Harry's hasty spell rebounds and hits Ron's leg.
One possibility could be that Percy's friends rally around him. They might take turns helping him with daily tasks like getting to class or bringing him food. His accident could also lead to some self - discovery, as he has to deal with being immobile for a while.
I'm not sure exactly how many TPN mangas there are. You might need to check reliable manga databases or the official publisher's information for an accurate count.
Definitely not. TPN is a work of fiction. The author came up with the concepts and storylines independently, without drawing from any true incidents. It's all about creative storytelling and fantasy.