Well, in this kind of fanfiction, a common plot is that Harry goes back to his earlier years at Hogwarts. He might try to stop Voldemort's rise from the very beginning. He could mentor his younger self, teaching him things he learned through all his previous battles. Also, he could change the way he interacted with the teachers. Instead of being a bit of a troublemaker in some cases, he could be more studious and use that to his advantage to gain more knowledge and power faster.
One interesting plot could be that Harry goes back in time and uses his future knowledge to prevent certain tragedies. For example, he might be able to save some characters who died in the original timeline. Another plot could involve him changing the relationships he had in the past. Maybe he could befriend those he was once enemies with or vice versa. He could also use his knowledge of magic from the future to outwit his past enemies in new and unexpected ways.
Obviously, Harry Potter is the main character. He is the one being sent back in time after all. Dumbledore often plays a significant role too. Since he was such an important figure in Harry's life, he might be the one to guide Harry in the new timeline. Hermione and Ron are also likely to be important. They were Harry's closest friends, and in the time - travel scenario, Harry might try to involve them in his new plans early on.
In certain fanfictions, Hermione could be sent back in time to improve relations between wizards and other magical creatures. She might start by helping Hagrid in his early days at Hogwarts, teaching him more about how to properly care for and protect the creatures. This could lead to a more harmonious co - existence between all magical beings in the wizarding world. By doing this, she could also change the way wizards view and interact with these creatures in the future.
In some fanfictions, Harry goes back in time and decides to train himself better. He could seek out different magical knowledge or combat skills that he didn't have the first time around, which then changes his future interactions and battles. For example, he might learn ancient spells that give him an edge against Voldemort.
One possible plot could be that Harry is under a spell that makes him believe he loves Voldemort and thus sends the love letters. This spell could be part of a larger plan by some dark wizard who wants to use Harry to get close to Voldemort and manipulate him. Another plot might be that Harry is actually trying to trick Voldemort with the love letters. He could be pretending to have feelings in order to lower Voldemort's guard and find a weakness in him.
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.
One interesting plot could be that they go back in time to prevent a certain dark wizard from ever rising to power in the first place. They might use their knowledge of future events to stop key events that led to the wizard's ascension.
One possible plot twist could be that Percy meets his own parents at a different time than expected. For example, instead of seeing his mother as he knew her, he might encounter her as a young girl. Another twist could be that Kronos has some ulterior motive for sending Percy back that Percy doesn't initially realize, like changing the course of events to actually benefit Kronos in the long run. Maybe Percy discovers that by changing certain events in the past, he's unknowingly setting up a different future that Kronos can manipulate more easily.
A common plot in such fanfictions is the idea that death has a plan for Harry that goes beyond what Dumbledore or anyone else expected. It could be that death wants to use Harry to balance the magical world in a different way. So, Harry might be led to discover ancient magic that is related to life and death, and he has to decide how to use it. This could involve making alliances with creatures that are associated with death, like thestrals or dementors in a different context.
One interesting plot could be Ichigo going back in time and preventing certain tragedies that happened in the original story. For example, he might stop the death of a beloved character, which would then change the entire course of events and relationships in the Bleach universe.
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 and his Death Eaters. Another plot could be Harry going back to his first year at Hogwarts and changing the way he interacted with certain characters like Snape, which could have a huge impact on the overall story. And he could also try to change the fate of some of the minor characters who died in the original story.