Hermione is often a very popular character. She's known for her intelligence and resourcefulness, and in fanfiction, she might come up with new spells or strategies to help Harry in his fight against Voldemort.
If Harry is the Master of Death in the fanfiction, the final battle with Voldemort would be a showdown on a whole new level. Harry would have a deeper understanding of the cycle of life and death. This could mean that he can manipulate the magic related to death in ways that Voldemort can't even comprehend. He could potentially disrupt Voldemort's connection to his Horcruxes, as he has a greater mastery over the essence of death that binds the Horcruxes. Moreover, Harry's power as the Master of Death could give him the ability to resurrect allies who have fallen in the battle against Voldemort, changing the tide of the fight completely.
One interesting plotline could be an alternate universe where Harry and Voldemort have to team up against a greater evil. This flips the traditional dynamic on its head.
In a Harry Potter final battle fanfiction, Harry might use some new and unexpected spells. For example, he could combine the Patronus Charm with a powerful offensive spell to repel the Death Eaters in a more spectacular way. Maybe he discovers a hidden power within himself that gives him an edge in the fight.
In this fanfiction, it could be that Voldemort has a premonition. He sees that if Harry Potter dies, it will lead to a series of disasters that will also destroy his own plans. So, in order to preserve the balance or to keep his long - term goals intact, he saves Harry. For example, if Harry's death causes an uncontrollable chaos in the wizarding world, Voldemort's rule over the dark forces might be disrupted. So he steps in to save Harry.
In many fanfictions, after the final battle, Harry might focus on rebuilding Hogwarts. He could use his influence to make it a more inclusive and modern place of magic learning, with new courses perhaps on Muggle technology and its integration with magic.
Obviously, Harry Potter is one of the most important. His role as the Chosen One is central to the final battle. Hermione Granger also plays a crucial part with her intelligence and knowledge of magic. Ron Weasley too, as he provides support to Harry.
The house - elves could be unsung heroes. In fanfiction, they might use their magic in ways that the wizards and witches don't expect. Since they are so good at household magic, they could turn that to their advantage in the battle. For instance, they could make the Hogwarts castle even more of a maze for the Death Eaters to navigate, or they could use their skills to quickly repair any damage done to the castle's defenses.
It could be Luna Lovegood. She has a unique perspective on magic. In the final battle fanfiction, she might use her strange but effective magical items and her unorthodox thinking to outwit Voldemort. For example, she could use some of her Lovegood family's special magical artifacts to create a shield or a trap for the Dark Lord.
It's possible. In the realm of fanfiction, the imagination knows no bounds. Writers might come up with such a scenario for various reasons, perhaps to explore a different side of the characters' relationships. But it's not a common or mainstream concept within the Harry Potter fanfiction community, as it goes against the typical character dynamics we expect from the series.