Hermione Granger could also be a rescuer. She was always intelligent and resourceful. In a fanfiction, she might figure out that Harry was in danger at the Dursleys' through some research or a hunch. Then she could use her knowledge of magic to break into the Dursleys' house and get Harry out. She would be brave enough to take on such a task to save her friend.
Dumbledore could be an unexpected ally. He might see this as an opportunity for Harry to stand up for himself and gain some closure on his difficult childhood. Also, some of the Hogwarts professors, like McGonagall, could be on Harry's side. They have always cared for Harry's well - being and would not tolerate the Dursleys' abuse. And there could be some new magical characters introduced specifically to help Harry in his legal battle, like a wizard lawyer who has a soft spot for underdog cases.
The main characters would be Harry Potter without a doubt. Since he is the focal point of the story as he is chained up. The Dursleys are key characters too. Vernon Dursley, with his mean - spirited nature, Petunia, who has always been cold towards Harry, and Dudley, who might have a change of heart during the story. And of course, we can't forget about Hedwig. She could be a crucial character, perhaps trying to bring help to Harry or at least provide some comfort while he is in such a dire situation.
There are fanfictions where a powerful wizard or witch, not part of the main Hogwarts faculty, discovers Harry's situation. Maybe an old hermit wizard who lives on the outskirts of the wizarding world. This wizard uses his magic to create a diversion at the Dursleys' place and then whisks Harry away to his own hidden cottage where he teaches Harry different kinds of magic not taught at Hogwarts.
One way could be through the intervention of a powerful wizard or witch who discovers Harry's mistreatment. For example, Dumbledore could send someone like Sirius Black earlier to rescue Harry. Another way might be if Harry himself discovers his magic earlier and uses it to escape. Maybe he finds a magical object in the Dursleys' house that helps him get away from their cruelty.
The main characters would surely include Harry Potter. He is the central figure in the Harry Potter series, and the story is about him being saved. The Winchesters, Sam and Dean, are also key. They bring their own set of skills and personalities from their own show. In addition, characters like Dumbledore might also play a role. He is the wise leader in the wizarding world and could either be aware of the Winchesters' presence or be clueless and later be impressed by their abilities to save Harry.
In some Harry Potter fanfictions, the Dursleys are depicted as nice. This could be a really interesting take. It might show how they could have been different if they hadn't been so influenced by their dislike for magic. Maybe they could have supported Harry more, or at least been less cruel. For example, a fanfiction could explore a scenario where Vernon Dursleys actually encourages Harry's academic achievements at school, instead of always putting him down.
One way the Dursleys can be good in fanfiction is if they are forced to face the consequences of their actions early on. For instance, they might receive a warning from the wizarding world that if they don't treat Harry well, there will be serious repercussions. So they start to be nicer to him. They could provide him with a proper room, better food, and allow him to have friends over.
Well, the Dursleys were really horrible to Harry. Fans want to see different ways he could have been saved. It also allows for new storylines. For example, if he's saved early, how would his magical development be different? How would his relationships with other characters change? All these possibilities make these fanfics interesting. Also, it gives a chance to explore different magical elements and characters in the context of rescuing Harry from the Dursleys.
One popular 'Harry Potter Saved from Dursleys' fanfic could be 'The Early Rescue'. In this fic, perhaps a powerful wizard discovers Harry's situation much earlier and takes him away from the Dursleys. Another might be 'A Different Start' where a magical creature intervenes and whisks Harry to a safe place away from his cruel relatives. There could also be 'Saved by the Unlikely' where a Muggle with some latent magical ability stumbles upon Harry and saves him from the Dursleys.
Hermione would likely be one of the characters. She's Harry's best friend and would probably try to find him and help him out. Ron might also be there, as he's always been by Harry's side. Dumbledore could be another character. He might be trying to keep an eye on Harry from afar, or perhaps he has a plan for Harry's new situation. Hagrid would also be a likely character. He has a soft spot for Harry and would want to make sure he's okay. And of course, the Dursleys themselves might make appearances, either to continue their mean - spirited ways or to have a change of heart.