A really cool plot for a Harry Potter time travel fanfic could be that a group of students, including Harry, Hermione, and Ron, travel back in time to the Triwizard Tournament era. But instead of just observing, they get involved in the tournament. Harry could team up with Cedric Diggory from the start and they work together to figure out the mysteries of the tournament. This would change the whole dynamic of the original story and lead to a different outcome, which in turn would have far - reaching effects on the future of the wizarding world.
Well, in a time travel fanfic, perhaps Harry accidentally travels back to the time when the founders of Hogwarts were still alive. He might learn ancient magic directly from them and use that knowledge to defeat Voldemort in his own time. Or Ron could go back in time and end up changing some Quidditch matches in the past, which then has unexpected consequences for the present, like different teams winning championships and changing the overall Quidditch culture at Hogwarts.
Another idea is that Harry travels to a time when his family was being hunted by Voldemort but in a parallel timeline. He could try to find a way to merge the timelines in a way that saves his family in both timelines. This would involve a lot of complex magic and decision - making on Harry's part.
In a 'Harry Potter Dark Time Travel Fanfic', a character could travel back to the time of the first great wizarding war. They could attempt to save lives that were lost in that conflict, but in doing so, they unknowingly create new threats. For instance, saving a certain wizard might lead to that wizard being corrupted later and causing even more destruction.
One idea could be that the next - generation characters travel back to the time of the first wizarding war. They could accidentally change some small events, which then have big consequences on their present time. For example, they might prevent a certain spell from being cast that was crucial in the defeat of a dark wizard, and now they have to figure out how to fix it in their own time.
One idea could be that the new generation discovers a time - turning device left by Hermione. They travel back to the time of the first Triwizard Tournament. There, they meet a young Sirius Black and Remus Lupin, and get involved in the mystery surrounding Cedric Diggory's death in a new way.
One idea could be that Harry travels back in time to his parents' era. He uses his mastery of death to protect them from Voldemort. Maybe he can't directly interfere but finds a way to subtly change things, like giving his father a special charm that ends up saving their lives in a crucial moment.
A third idea might be that both Harry and Teddy accidentally travel to a time in the past where a great magical event took place, like the founding of Hogwarts. They have to figure out how to get back to their own time while also trying not to disrupt the events that are crucial to the wizarding world's history. They might even learn some long - lost spells or magical knowledge during their time there.
Perhaps the phoenix can travel through time as well in this fanfic. Harry travels back in time with the phoenix to a crucial moment in the wizarding world's history. He has to make sure not to disrupt the timeline while also learning something that can help in his present fight against the dark forces.
Perhaps a fan fic where a student travels back to the time of the founders of Hogwarts. They could witness the creation of the houses and the laying of the school's foundation, and even interact with the founders, which would be really cool.
Well, perhaps the time - traveling protagonist has a special ability that gets noticed by different female characters. Say, the ability to manipulate time in unique ways. Harry Potter characters like Cho Chang could be part of the harem. The time traveler could be from a future where the wizarding world is in chaos, and by traveling back, they try to change things. This draws the attention of various characters, who then form a harem around the time traveler as they all work towards a better future for the wizarding world.
A possible plot in the Harry Potter Teddy time travel fanfiction could be Teddy going back to the time of the founders of Hogwarts. He could be a sort of mediator between the four founders, especially if there were some disputes or misunderstandings that led to future problems in Hogwarts. Teddy could use his knowledge from the future to try and smooth things over. This would not only change the history of Hogwarts but also have a big impact on the future wizarding world he comes from.