Another plot could focus on Harry's relationship with Cedric Diggory before the tournament. Maybe they become friends secretly and help each other out with the tasks, adding a new layer to the competition.
One idea could be exploring more of the backstories of the other schools' students who came for the Triwizard Tournament. For example, delving deeper into the life of a Durmstrang student and how their magic education differs from Hogwarts.
A really interesting plot would be if there was a mystery surrounding the Goblet of Fire that was not in the original story. Like, there could be a hidden charm on it that was placed by a dark wizard long ago, and this charm starts to affect the tournament in unexpected ways.
Another interesting plot could be that Harry's connection to Voldemort causes some strange magical disruptions during the Triwizard Tournament. These disruptions seem like accidents at first, but Harry gradually realizes they are being caused by his own dark - side related powers that are being awakened in his fourth year.
A fanfiction could also be about Harry's relationship with his parents during his fourth year. Through some magical event, he gets to communicate with their spirits or memories more vividly. This could help him understand his parents better and also give him strength and guidance for the challenges he faces in that year.
Maybe in this 4th - year fanfiction, Harry and Hermione get involved in a Triwizard Tournament - like event but for younger students. They face challenges that test not only their magical skills but also their friendship. For example, one challenge could be to rescue a 'hostage' (a magical creature) from a dangerous enchanted forest without using their wands.
One idea could be that Harry discovers a new, hidden magical ability within himself that helps him in the final battle against Voldemort. For example, the ability to communicate with the spirits of Hogwarts founders for guidance. Another could be that the relationships between the characters take a different turn. Maybe Hermione and Ron have a huge fight early on and Hermione teams up with Draco for a while out of necessity, which changes the dynamics of the whole group. Also, Neville could have an even more prominent role, leading a secret group of students who are training in a new form of magic that they hope will give them an edge in the fight.
A plot could be that Harry has premonitions about the Triwizard Tournament tasks before they happen. These premonitions are not clear at first, but as he gets closer to each task, he starts to understand them better. It adds an element of mystery and foreshadowing to the story.
A great plot could be focusing on the love triangle between Harry, Ginny, and Hermione. Harry might struggle with his feelings for Ginny while also being really close to Hermione, and this could create some interesting drama and tension. Also, it could tie in with the events of the 6th year like the search for Voldemort's Horcruxes.
Well, in some 'Harry Potter 8th book fanfiction', a cool plot is that the magic in the world starts to fade and Harry, along with his friends, has to find the source of this problem. It could also be about the children of the main characters having their own adventures at Hogwarts, but with a new, even more dangerous threat lurking in the shadows. Maybe there's a plot where the Ministry of Magic is corrupted again and the old heroes have to step in to clean it up once more.
Another plot could involve Draco forming an unlikely alliance during his 6th year. For example, he teams up with a Muggle - born student to solve a mystery within the school walls. This would show his growth and changing perspectives. As he gets closer to this student, he starts to question the pure - blood ideology he was raised with.
A really cool plot twist might be that Hermione finds a way to travel back in time to change certain events that led to Voldemort's rise. She has to be extremely careful not to disrupt the whole timeline while trying to save the wizarding world. It's a complex and exciting idea that can lead to a lot of interesting scenarios in the 7th year of the story.
Perhaps in the fanfiction, we could see a different side of the foreign students. Like, the Beauxbatons and Durmstrang students could have their own hidden agendas. One of them might be in love with Harry and tries to protect him during the tournament tasks. This would create a whole new dynamic of relationships and loyalties within the story.