Well, one plot idea could be that Hermione accidentally gets entered into the Triwizard Tournament instead of Harry. This would change the whole dynamic as she would have to face the dangerous tasks, and Harry would be in the role of her supporter and strategist.
Another idea is that the Goblet of Fire is actually a cursed object that is slowly influencing the whole school. Harry and Hermione figure this out early on and have to find a way to break the curse before the tournament goes horribly wrong. They might have to go on a secret mission to find the origin of the curse, and along the way, they discover secrets about the founders of Hogwarts.
A unique plot could be that Harry and Hermione find a time - traveling spell within the Goblet of Fire. They use it to go back in time to the previous Triwizard Tournaments to learn more about the history and secrets of the event. But as they do this, they risk changing the present and future, and they have to be very careful about their actions.
Well, a plot could involve Harry and Hermione being forced to enter the tournament together as a pair, against the rules. They then have to face challenges that are not only dangerous but also designed to test their relationship. For example, in one task, they might have to choose between saving each other or winning the task. This would create a lot of drama and tension between them. Also, there could be a sub - plot where they start to realize their feelings for each other during the tournament.
Another plot could involve Hermione using her vast knowledge to help Harry train for the tasks in the tournament in a more unique way. For example, she might find a way to combine ancient magic with modern spell - casting techniques. This could lead to some really exciting and unexpected moments during the tasks.
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.
Another idea is that Snape could be the one who discovers a plot by a Death Eater to use the Triwizard Tournament to bring Voldemort back in a more powerful form. Snape then has to decide whether to take matters into his own hands or trust Dumbledore with this information. This would create a lot of tension and drama as Snape is not one to easily trust or be trusted.
One interesting plot idea could be exploring what would happen if a different student was chosen for the Triwizard Tournament. Maybe a shy and overlooked student gets picked, and they have to overcome not only the tournament tasks but also their own insecurities. Another idea could be a love triangle involving characters that were not part of one in the original story. For example, a friendship between a Hufflepuff and a Slytherin turns into a complex relationship when feelings for Harry Potter get involved.
One fanfic that comes to mind is 'Hermione's Unforeseen Adventure in the Goblet of Fire'. In this fanfic, Hermione accidentally switches places with one of the champions in a magical mishap. She has to then compete in the tasks while trying to figure out how to reverse the spell. It's a really unique take on the Goblet of Fire story.
Well, it could be that Hermione accidentally drinks a love potion during the Goblet of Fire events. Harry is the only one who can break the spell. The 'lemon' aspect might be some flirty and slightly spicy interactions as Harry tries to bring Hermione back to normal. For example, a scene where Harry has to hold Hermione's hand a bit longer than necessary while reciting a counter - spell.
One idea could be exploring what would happen if a different student was chosen by the Goblet of Fire. Maybe a Muggle - born student who has to face extra prejudice during the Triwizard Tournament. It would add a new layer of conflict and show how the wizarding world reacts to a 'less likely' champion.
One idea could be that the OC is a foreign exchange student who has unique magical abilities unknown to Hogwarts. They could help Harry in the Triwizard Tournament tasks in unexpected ways, like using ancient spells from their home country.
One idea could be that Harry has a group of friends from different houses who are all secretly in love with him. They start to form a sort of harem around him during the Triwizard Tournament. For example, Hermione could be using her intelligence to help him in the tournament in a more personal way, and Cho Chang might be more openly affectionate, and then there could be a girl from Beauxbatons who is also drawn to Harry's bravery.