Perhaps there is a prophecy that the Death Eaters misinterpret at first. They think killing Harry is the right thing, but later they discover that saving him is actually crucial for their own survival or for some greater good in the wizarding world. So they decide to go against Voldemort's orders and save Harry. For instance, they find out that Harry has some power that can prevent a much greater evil from emerging, which would also threaten the Death Eaters.
It could be due to a personal connection. There might be a Death Eater who has a family member or a loved one who is somehow related to Harry. Maybe Harry unknowingly saved that person in the past, and the Death Eater feels indebted to him. So, in order to repay the debt, the Death Eater risks everything to save Harry from a dangerous situation.
A possible motive could be self - preservation. If they believe that Voldemort's downfall is inevitable and that by saving Harry, they can gain some form of leniency from the side that opposes Voldemort. They might think that Harry has enough influence to spare their lives if they help him.
One way this could happen is if Harry Potter discovers a new form of magic that can reverse the dark magic influencing the Death Eaters. Maybe he finds a powerful spell during his exploration of ancient magic that can purify their souls and free them from Voldemort's control.
One possibility is that some Death Eaters might have a change of heart. Maybe they see the true evil of Voldemort's cause. For example, a Death Eater who has a family member saved by Harry could decide to help. They could secretly pass on information about Voldemort's plans to Harry. In the complex world of the Harry Potter universe, personal motives and moral awakenings can be strong forces.
Hermione could resist the Death Eaters with her vast knowledge of magic. For example, she could use protective spells and charms she has learned from her studies. She might also use her quick thinking to outwit them in verbal exchanges, not giving them any information or advantage.
Maybe the Death Eaters save Harry, but then they try to use him as a bargaining chip. They think they can trade Harry's safety for something they want, like amnesty or a powerful magical artifact. However, things don't go as planned and they end up having to truly protect him.
Voldemort himself, of course, is the most prominent in a sense. But in the fanfiction, his relationship with the other Death Eaters could be different. He might be more distrustful or have different expectations of them. And then there's Barty Crouch Jr. He could be a major player in the fanfiction, with his skills in disguise and dark magic. His actions could drive some of the major plotlines in the fanfiction.
In this kind of fanfiction, the plot would deviate a great deal. Harry's motivation would change. Instead of fighting against Voldemort, he could be fighting to uphold the Death Eater ideology. His adventures at Hogwarts would be focused on different things, like learning more powerful Dark Magic. His encounters with magical creatures might also be different. He might use them for more sinister purposes rather than just for the sake of knowledge or protection as in the original story.
A possible plotline could be that a Death Eater discovers Hermione has knowledge of a powerful spell or magic item that could help them overthrow Voldemort. So, they save her to get that information. For example, she might know of a way to break a powerful curse that Voldemort has placed on them.
Well, perhaps in this fanfiction, there's a big misunderstanding. Harry might think that by infiltrating the Death Eaters as one of them, he can actually bring them down from the inside. So he pretends to join them, but things get out of hand as he has to constantly prove his loyalty to the dark side, which is really difficult for him.
The impact on the Harry Potter fandom would be quite significant. On the positive side, it could bring in new fans who are interested in this kind of no - holds - barred approach to dealing with the Death Eaters. It can also fuel creativity as other fanfiction writers might build on this idea or create counter - stories. However, there will be those in the fandom who are very attached to the original narrative and will see this as a desecration of the carefully crafted world. They might feel that it undermines the growth and development of the characters and the complex relationships within the story. This could lead to debates and discussions within the fandom, which in a way also keeps the fandom alive and active.