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.
Well, in some 'Harry Potter sent back in time' fanfictions, Harry might go back to the time when the Marauders were at Hogwarts. He could then join their adventures, and perhaps use his future knowledge to help them out. He might also try to save Sirius from being wrongly imprisoned later. It's really fascinating to think about how he could impact the past and change the future in these stories.
One interesting plot twist could be that Harry goes back in time and accidentally changes the sorting of some of the characters. For example, Draco Malfoy could end up in Gryffindor instead of Slytherin, which would completely change their relationship and how events unfold in the wizarding world.
Well, in some fanfictions of this kind, Harry might face a cruel caretaker in the orphanage. But instead of being beaten down, he uses his wits and hidden magic to stand up for himself and the other kids. He could also start to learn magic on his own, using his natural instincts, which would be a really cool plot.
In this type of fanfiction, a great plot can be Naruto going back and influencing the Third Hokage's decisions. For example, he could convince the Hokage to be more open - minded about new techniques and alliances. He might also focus on improving the living conditions in the village at an earlier stage. By doing so, he could potentially change the future of the entire Hidden Leaf Village and the shinobi world in general.
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 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 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.
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.
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.
Harry himself is obviously a very popular character in these fanfictions as he is the one being sent back in time. But also, characters like Sirius Black are often popular. Fans like to explore how Sirius would react to Harry being in the past, and how their relationship could develop differently.
Definitely Harry himself. Since he is the one being sent back in time, he is central to the story. His actions and decisions in the past are what drive the plot forward.