The plot could also involve the other characters' reactions to this evil version of Naruto from the future. Some might be confused, while others might immediately sense the danger. Naruto could also face challenges in changing the past as there could be unforeseen consequences or time - related ninja techniques that prevent him from fully achieving his evil goals.
His relationship with Sasuke would be very different. If Naruto stops the Uchiha massacre, Sasuke may not have the intense hatred he had in the original story. They could grow up as friends without the need for Naruto to constantly chase after Sasuke to bring him back.
The main antagonists could be the original Naruto's friends and allies. Since this is an evil Naruto, people like Sasuke, Sakura, and Kakashi would likely oppose him and try to stop him from whatever evil plans he has in the past.
One popular plot twist could be Naruto preventing the Uchiha massacre. This would completely change the future as Sasuke's path of revenge would be derailed. It would also impact the relationship between the Uchiha and the rest of the village.
Sasuke is also very popular. As Naruto's friend and rival, many fanfictions explore how their relationship would be different if Naruto had a second chance. For example, Sasuke might be more open to Naruto's friendship earlier due to Naruto's new approach influenced by his future knowledge.
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.
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.
Another plot could be that Bella is sent back in time by some magical force related to Elijah. When she arrives, she finds Elijah in a difficult situation, like being trapped by an enemy. Using her wits and any powers she might have, she helps him escape. This starts a chain of events where they become allies and then, over time, more than that. They might travel through different historical events together, with Bella always having the knowledge of the future in the back of her mind to help them out.