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.
Harry is the central figure here. But other characters like Cedric Diggory could be involved. Since Cedric is a Triwizard Champion, if Harry messes with the goblet, it could directly or indirectly affect Cedric. Also, the teachers like Professor McGonagall might play a role. She would be concerned about Harry's actions and try to keep Hogwarts in order. There could also be appearances from the other schools' representatives as they are all connected to the Goblet of Fire and the Triwizard Tournament.
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.
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.
It could be Sirius Black. He has a lot of experience in the wizarding world and, despite being on the run, he could find a way to communicate with Harry secretly. He could teach Harry about dark magic defense, which would be very useful in the tournament.
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.
A possible plot could be that the Goblet of Fire starts acting strangely. McGonagall notices some odd magical fluctuations around it. She enlists the help of Hermione, knowing her academic prowess. Together they try to figure out what's wrong. Meanwhile, Harry has a strange feeling about it all. Eventually, they discover that a dark wizard from the past is trying to use the Goblet to return. And they must stop it before it's too late.
One interesting plot twist could be a different champion being secretly controlled by Voldemort instead of just Barty Crouch Jr. as the imposter Moody. Maybe a champion from a different school who no one suspects.
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.