A really interesting plot could be based on a time - travel aspect. A fanfic could have a character go back in time to try and prevent certain events that led to the start of the Deathly Hallows story. Maybe they try to stop Snape from making that fateful decision that set everything in motion. This would completely change the course of the story and could lead to all kinds of new and exciting plot twists.
Another plot idea could be a different take on the journey of Harry, Ron, and Hermione. What if they got separated early on in their quest for the Horcruxes? Each of them could then have their own mini - adventure, facing different challenges and making new allies. Harry might find a group of magical creatures that help him in an unexpected way, Ron could stumble upon a hidden wizarding community that has knowledge about Horcruxes, and Hermione could encounter a powerful witch who has her own vendetta against Voldemort.
Another plot could involve Ron's relationship with his family during the events of the Deathly Hallows in the fanfic. His family has always been important to him, and perhaps in this story, he has to make a difficult choice that could impact his family's safety. He might have to decide between following Harry on a dangerous mission or staying back to protect his family, which could lead to some really emotional and tense moments.
One idea could be exploring the new generation at Hogwarts. Maybe a character discovers a hidden spell that was forgotten during the main series and it has unexpected consequences for the wizarding world. Another could be about the rebuilding of the wizarding community after the war, focusing on how different families reunite and deal with the losses they've suffered.
A new character could be an ancient wizard who has been in hiding for centuries. He could have knowledge about the Deathly Hallows that even Dumbledore didn't know. This character could appear to Harry and his friends and offer them guidance or a powerful magical artifact that helps them on their journey.
One idea could be exploring what would happen if Neville found the Deathly Hallows instead of Harry. He has shown great courage throughout the series and it would be fascinating to see how he would handle that power.
One idea could be exploring what would happen if Neville Longbottom was the one who had to face Voldemort in the final battle instead of Harry. Another could be a fanfiction where the Deathly Hallows were discovered in a different order and how that changes the course of the story. Or perhaps a story about the Marauders' era characters influencing the events of the Deathly Hallows from the afterlife.
A really out - there plot twist in fanfiction could be that the Deathly Hallows themselves have a different origin or purpose than what was originally thought. For example, the Elder Wand might be a key to a whole new realm of magic that Voldemort was unaware of, and Harry uses this knowledge to his advantage in the battle against the Dark Lord.
One interesting plot idea could be that Harry and Hermione discover a hidden spell within the Deathly Hallows that allows them to time - travel briefly. They use this to go back and change a small but crucial event in the war against Voldemort, which has a big impact on the final outcome. Another could be that they find a secret chamber within the Hallows that holds the lost memories of some of the greatest wizards of all time, and these memories give them the knowledge to defeat Voldemort in a completely unexpected way.
Maybe in the fanfiction, the Deathly Hallows have a connection to an ancient prophecy that only Harry and Hermione can decipher. This prophecy reveals a way to bring true and lasting peace to the wizarding world. So they have to race against time, with the Death Eaters hot on their trail, to figure out the meaning and fulfill the prophecy.
One idea could be exploring how the wizarding world rebuilds after the war. Harry, Ron, and Hermione could take on leadership roles in different aspects, like Harry in Auror training reform, Ron in Weasley's Wizard Wheezes expansion to help heal through humor, and Hermione in magical education reform to include more about Muggle - born history. Another could be a story about the next generation at Hogwarts, with Harry's kids and their friends facing new, non - Voldemort - related challenges but still learning from the past.
One interesting fan fiction could be about Neville leading a secret resistance within Hogwarts during the Deathly Hallows time. He uses his knowledge of the castle and plants to outwit the Death Eaters. Another could be a story where Neville discovers a hidden power related to the Deathly Hallows that gives him an edge in the final battle. And there might be a fan fic that focuses on Neville's emotional journey during this dark time, like his internal struggle with fear and his determination to fight for his friends.