One possible plot could be Anakin going back to a time before his fall to the dark side. He could use his knowledge of the future to prevent certain tragedies. For example, he might stop the Clone Wars from starting, thus saving countless lives. This would also give him a chance to redeem himself and perhaps even change the fate of the Jedi Order.
Obviously, he would interact with his younger self. He could try to guide his younger self, offer advice on how to control the Force better and how to deal with the temptations of the Dark Side.
In this fanfic scenario, Anakin's character would develop with a greater sense of purpose. He would no longer be a victim of fate. He could take control of his destiny. He would be more self - assured, knowing what lies ahead. His relationships with other characters would also be different. He would be more of a leader, guiding others based on his future knowledge. This would transform him into a more positive and influential figure in the Star Wars universe.
Perhaps he goes back in time and decides to train himself better. He could focus on mastering his emotions from the start, which might change the entire course of the Star Wars saga. He might also try to save his mother in a more effective way, without succumbing to anger and hatred.
There could be a hermit or an outcast Jedi or Sith on Dathomir. Anakin meeting this character could lead to a great revelation. Maybe this character has been in hiding on Dathomir for years, observing the balance of the Force there, and Anakin's arrival disrupts that balance and forces an interaction that changes Anakin's perspective on many things.
One possible plot twist could be Anakin going back in time and preventing his own fall to the dark side. He might use his knowledge of the future to avoid the events that led him to become Darth Vader. For example, he could avoid the temptation of Palpatine's offers. Another twist could be that his time - traveling disrupts the Force in unexpected ways, causing new alliances and enmities to form. Maybe he accidentally changes the course of other Jedi's lives, leading to a completely different galactic power structure.
Anakin's time travel could lead to a completely different relationship with Padmé. He may realize that his obsession with her in the original timeline was part of what led him down the dark path. So, instead of repeating the same pattern, he could focus on being her friend and protector in a more platonic way. This new dynamic might not only change their relationship but also have a significant impact on Anakin's overall character development and his place in the galaxy.
In the 'Percy goes back in time fanfic', he may also meet his younger self. This could lead to some really interesting and confusing situations. He would have to be careful not to disrupt the timeline too much while still achieving whatever his goal is for going back in time.
His friends from his normal time period could also be important. They might be the reason he decides to go back in time in the first place, like to save one of them from a past danger.
There are many fanfics that play with the idea of time travel. For Bella going back in time to meet Jasper, the story could explore how their prior knowledge of each other in the future affects their initial meeting in the past. For example, does Bella already trust Jasper because she knows him from the future? This could create a really unique dynamic in the story.