A possible plot is that Harry gets angry at the unfair treatment he receives during the tasks of the Goblet of Fire. For example, in one task, he might notice that the other champions have some advantages that he doesn't. His anger then gives him the motivation to find a way to overcome these unfair situations and still succeed in the tournament. He could use his anger to fuel his creativity and come up with unique solutions to the challenges.
Perhaps a fanfiction where Harry is angry due to the danger the Goblet of Fire has put his friends in. He realizes that just by being a part of the Triwizard Tournament, his enemies might target his friends to get to him. His anger could drive him to take extra precautions to protect them, and also make him more determined to succeed in the tournament so that he can prove that he's not a coward and that he can handle whatever comes his way.
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.
A possible plot could be that adult Harry is called back to Hogwarts due to some strange magical disturbances related to the Goblet of Fire. He realizes that there are remnants of dark magic from the tournament that were never fully eradicated. He then has to work with the current Hogwarts staff and students to find and neutralize these dark magic sources.
The fanfic might revolve around Harry's interaction with the Goblet of Fire due to a misunderstanding. He could think that the goblet is being influenced by dark magic and decides to investigate. As he messes with it, he discovers some hidden secrets about the Triwizard Tournament and its origins. This could lead to him having to make difficult choices to protect the integrity of the tournament and Hogwarts, all while dealing with the consequences of his meddling with such a powerful magical object.
One possible consequence could be that he'd be seen as a rule - breaker on a whole new level. The Goblet of Fire is a very important magical object in the wizarding world. Its destruction might lead to chaos in the Triwizard Tournament. For example, the tasks could become unstructured or the magic binding the tournament together could start to unravel.
Perhaps Harry is transported to a time in the past during the Goblet of Fire event. He could interact with the founders of Hogwarts, and they could give him advice on how to deal with the dark forces that are at play in his own time. This would add a historical and magical depth to the fanfic.
One possible plot could be Harry discovers a hidden training ground within Hogwarts. He meets a mysterious old wizard there who teaches him unique spells and combat techniques specifically for the Triwizard Tournament tasks. This wizard could have some connection to the founders of Hogwarts, and his teachings give Harry an edge in the tournament.
One interesting plot twist could be that Harry has an unexpected ally in the Triwizard Tournament. Maybe a Slytherin student who has a hidden agenda but ends up helping Harry in a crucial task. This would change the dynamic of the traditional House rivalries.
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 interesting plot in this kind of fanfiction could be that the Goblet of Fire is actually under some dark magic influence. Harry, being summoned, discovers this conspiracy. He then has to not only deal with the Triwizard Tournament tasks but also find a way to break the dark magic's hold on the Goblet. This could involve him delving deeper into ancient magic lore and seeking help from the Forbidden Forest's creatures that are often overlooked in the original story.