Well, Harry Potter would most likely be one of the main characters. He is Hermione's close friend and they often face challenges together in the original series, so it's reasonable to assume he'd play an important role in the fanfic as well.
Often, you'll see original characters who are students from other schools. For example, there might be a really smart and mysterious student from Durmstrang who becomes friends or rivals with Hermione. They could have their own motives for being at Hogwarts during the Goblet of Fire events.
One interesting plot twist could be that Hermione is secretly entered into the Triwizard Tournament not by the Goblet, but by a dark wizard who wants to use her as a pawn. This would put her in a very dangerous situation right from the start.
One interesting plot twist could be that Hermione discovers a hidden spell within the Goblet of Fire that no one else knew about. This spell could change the nature of the Triwizard Tournament in unexpected ways.
One interesting Hermione in Goblet of Fire fanfic could be one where she has to solve a mystery related to the Triwizard Tournament that the original story didn't cover. For example, she might discover a hidden plot by a group of dark wizards who are trying to manipulate the tournament for their own evil purposes. Another could be a fanfic that focuses on Hermione's relationship with other characters during that time, like a deeper friendship with Cedric Diggory. She could be helping Cedric prepare for the tasks in ways that the books didn't show.
One great fanfic could be about Harry and Hermione getting unexpected advice from McGonagall regarding the Goblet of Fire. Maybe McGonagall suspects some foul play early on and warns them to stay away from it, but their curiosity gets the better of them.
Yes, it can be a somewhat common theme. In fanfiction, writers often explore different relationship dynamics that weren't fully developed in the original 'Goblet of Fire' story. Some fans might be intrigued by the idea of Hermione and Harry having a more romantic connection, so they write about Hermione kissing Harry to create new and interesting storylines.
One interesting fanfic could be where Harry and Hermione team up to solve the mysteries behind the Goblet of Fire in a more in - depth way than in the original book. Maybe they discover a hidden plot early on and work together to expose it.
One common theme is friendship deepening into something more. In many fanfictions, the events of the Goblet of Fire bring Harry and Hermione closer together in a way that makes them realize their feelings for each other go beyond just friendship. Another theme is the exploration of the magical elements. Since the Goblet of Fire is full of magic, fanfictions often expand on the magic in unique ways, like new spells or hidden magical artifacts related to the tournament.
One great 'Harry Hermione Goblet of Fire' fanfiction is 'The Unforeseen Bond'. It delves into their relationship during the events of the Triwizard Tournament. It shows how Hermione supports Harry in a more in - depth way than in the original story, and there are some really interesting plot twists that make it a captivating read.