Perhaps a story where a character uses a magical time - turner in a new way. Instead of going back a few hours, they accidentally travel decades into the past and have to find a way to return while not disrupting the timeline too much. They might meet young versions of their professors and see how different Hogwarts was back then.
One interesting plot could be time - traveling to the founders' era. The characters might witness the creation of Hogwarts and interact with the founders. They could learn the original intentions behind the house system and the hidden secrets of the castle.
One interesting plot could be how the characters' magical abilities develop during puberty. For example, Harry might discover new powers related to his connection with Voldemort as he grows older. Another could be the relationships between the characters changing due to the hormonal shifts of puberty. Hermione might become more confident and assertive in her magical studies and interactions with others.
Another plot could involve Harry traveling to a different magical realm in search of a master who can teach him advanced skills. There, he meets all sorts of strange and powerful wizards. He has to prove himself worthy by competing in a magical tournament where the prize is the knowledge of grinding skills to an extraordinary level.
One interesting plot could be a character going back in time in the Time Chamber to prevent a major tragedy that happened in the wizarding world. For example, they might try to stop the first rise of Voldemort.
A plot could be that James Potter travels back to the time when Voldemort was still Tom Riddle at Hogwarts. He could try to influence Riddle in a positive way, perhaps by befriending him and showing him a different path than the dark one. However, he has to be careful not to change the future too much or risk endangering his own existence and that of his family.
In some Harry Potter 8 fanfictions, there are plots where the characters continue to face new dark magic threats. For example, a new dark wizard might emerge, and Harry, Hermione and Ron have to use their combined skills and knowledge to defeat this new foe. Another plot could be about the exploration of the wizarding world's past in more depth, revealing secrets that were previously unknown.
One interesting plot could be Harry going back in time to prevent the death of his parents. He might use his knowledge of future events to outwit Voldemort before he becomes too powerful. Another could be Harry traveling back to his first year at Hogwarts and changing how he interacted with certain characters like Snape, which could lead to a different dynamic between them throughout the series.
One interesting plot could be a character going back in time to prevent Voldemort's first rise to power. They could try to change the events that led to his initial gathering of followers. Another plot might involve a time - traveling student who accidentally alters the sorting of the houses, causing chaos and new alliances within Hogwarts. And a third could be a time traveler going back to the Marauders' era and getting involved in their pranks and adventures, which in turn has unforeseen consequences for the future.
One interesting plot could be Harry going back in time and preventing certain tragedies from happening in the wizarding world, like stopping Voldemort's rise before it really began. Another could be him changing the relationships between characters, for example, making Snape and James Potter become friends early on.
Maybe in the fanfiction, Harry uses the Time - Turner to train with long - dead great wizards. He travels back in time to learn from Merlin himself. Merlin could teach Harry ancient and powerful magic that has been lost over the centuries. This would give Harry an edge in his fight against Voldemort and also expand his understanding of the wizarding world's history.
One interesting plot could be the characters going back in time to prevent certain dark magic events from ever happening. For example, they might stop Voldemort's rise to power much earlier in history.