She could meet her younger self. This would be an interesting encounter as she could offer advice and guidance to her younger version. Maybe she could help her younger self to be less afraid of her powers.
One possible plot could be Serena going back in time to prevent a major disaster in her world. For example, she might go back to stop an evil force from being released. In the past, she could meet younger versions of her friends and family, and they might not recognize her at first. She would have to use her knowledge from the future to try and change things for the better.
In the 'Petunia Goes Back in Time' fanfiction, she might try to change things that happened in the past. Maybe she wants to fix a mistake or prevent a bad event from occurring.
One possibility is that Draco could try to change his family's fate. In the original story, his family was on the wrong side of the wizarding war. By going back in time, he might attempt to steer them towards a more positive path, perhaps by preventing them from getting involved with Voldemort in the first place.
One common theme is redemption. For example, Rey might go back in time to redeem a character who has fallen to the dark side. Another theme is the exploration of 'what if' scenarios. Like what if Rey changed a certain event in the past, how would it affect the future of the Star Wars universe.
He might change the course of some major battles. For example, he could prevent the destruction of certain planets that were destroyed in the original timeline.
Perhaps Elsa goes back in time to meet her parents again. She could learn more about her powers from them, as they might have known more than she initially thought. This encounter could also give her a chance to say goodbye properly, which she didn't get the first time. And it could lead to her having a better understanding of her place in the kingdom and her family.
One common theme is redemption. Hiro might go back in time to right his wrongs or the wrongs of others. Another theme is self - discovery. By going back in time, he can learn more about himself and his family history.
In this fanfiction, Nero might change historical events. For example, he could prevent certain disasters or alter the fates of key characters. Maybe he'll meet his ancestors and learn secrets about his family's past.
In this fanfiction, Gohan might change important events in the past. For example, he could prevent certain villains from getting stronger or save characters who died previously.