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.
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.
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.
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.
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 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.
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.
One idea could be a character going back in time to prevent a major dark wizard event that was overlooked in the original series. For example, they might try to stop the initial rise of Voldemort before he became so powerful.
Well, perhaps Harry travels back in time to the very beginning of the wizarding world. He discovers secrets about magic that have been long forgotten. He then uses this knowledge to make the wizarding world more inclusive and less divided by blood purity. Or he could time - travel during his own time period, like going back to his first year at Hogwarts over and over again to change small things that have big consequences in the future, like making sure Neville is more confident from the start.
Another plot could be that they travel back to the time when the Chamber of Secrets was first opened. Ginny, having been possessed by Tom Riddle in her own time, could use her knowledge to stop the young Voldemort from causing so much harm. Harry could also help by using his skills and knowledge of magic from his own time to combat the basilisk and keep students safe.
Well, a plot could be that a character from the future, like a descendant of Harry Potter, travels back in time to the time of the Triwizard Tournament. This character could have some knowledge of future threats and tries to prevent certain events during the tournament that could lead to greater disasters in the future. They might try to stop Voldemort's minions from using the tournament as a cover to carry out their evil plans. They could also try to make sure that Cedric Diggory doesn't die, which would have a huge impact on the wizarding community as he was a very popular and promising young wizard.