One interesting plotline could be a deeper exploration of the Triwizard Tournament tasks from a different perspective. Maybe showing the behind - the - scenes preparations by the champions that we didn't see in the original book. Another could be a new relationship developing between characters, like a friendship between a Hogwarts student and a Durmstrang student that impacts the events of the tournament.
Well, in some Harry Potter 4th year fanfic, there might be a plotline where the Goblet of Fire's selection process is tampered with in a more complex way. Instead of just Barty Crouch Jr.'s simple plot, there could be multiple parties involved. Also, there could be a fanfic that focuses on the Yule Ball and the drama that unfolds not just between the main characters but also among the minor characters, like how some students from different houses interact during the ball.
A great plotline in Harry Potter 4th year fanfic could be the expansion of the character of Cedric Diggory. Fanfic authors might give him more backstory, like his family history and how it influenced his actions during the Triwizard Tournament. Some fanfics could also explore what would have happened if Cedric had survived the graveyard scene and how it would have changed the course of the story. There could be a plot where he teams up with Harry to fight Voldemort later on, using the knowledge he gained from that fateful encounter.
In many Harry Potter 8th year fanfic plotlines, the exploration of the wizarding world outside of Hogwarts becomes a major focus. Harry and his friends could be traveling to different wizarding communities, learning about their cultures and magic. They might encounter new magical creatures and have to figure out how to interact with them. There could also be a mystery involving a powerful, ancient magic that is somehow related to their 8th year at Hogwarts, and they have to solve it to keep the wizarding world safe.
One interesting plotline could be Harry dealing with the aftermath of the war in Hogwarts. He might be trying to heal the school and its students from the trauma. Another could be his relationship with Ginny evolving further as they face new challenges together in their final year.
One interesting plotline could be exploring more of Snape's inner turmoil during Harry's 6th year. Maybe showing his secret efforts to protect Harry while still maintaining his cover among the Death Eaters.
One interesting plotline could be Harry's struggle with his new role as a leader in Dumbledore's Army. He has to deal with the pressure of teaching his peers and also keeping the group a secret from Umbridge.
A possible plotline could be that Hogwarts itself becomes a sort of magical battleground earlier than expected. The Death Eaters try to take over the school completely, and the students and remaining teachers have to fight back in a sort of guerilla warfare within the castle walls. This would change the whole dynamic of the seventh year, with classes being interrupted and students having to use their magic in real - life combat situations.
One interesting plot could be about Harry forming an unexpected alliance with some Slytherin students during his 5th year. They might team up to uncover a mystery within Hogwarts that involves a dark magic item that was planted there by Death Eaters. This could lead to a lot of character development as they learn to trust each other despite their house differences.
In 4th - year Harry Potter fanfics, a popular plot is Harry's training for the Triwizard tasks. He could be getting secret help from an unexpected source, like a former champion or a hidden teacher at Hogwarts. His relationship with Cedric Diggory can also be a major part of the story. It might start as a rivalry but develop into a mutual respect. Plus, the way the fanfic portrays the magic in the tasks, like the underwater scene in the second task, can be really interesting and unique to each writer.
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.
One interesting plot twist could be that a minor character from the previous years turns out to be a key figure in the fight against Voldemort. For example, a Hufflepuff student who was always in the background might have some secret knowledge or power that helps Harry in his final battle.
In some fanfictions, there could be a plotline where Harry and Hermione start to realize their feelings for each other in a different way during their 6th year. They've been through so much together, and this year could be the turning point where their relationship evolves from just friendship. They might have more private moments, sharing their fears and hopes, and this newfound closeness could lead to a whole new dynamic in their relationship.