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.
One great 'Percy sent back in time' fanfic is 'Back to the Beginning'. It shows Percy having to deal with all the early threats in a new way. Another is 'Time - Twisted Percy' which has an interesting take on how his knowledge of the future changes things. There's also 'Percy's Time - Travel Adventure' where he forms unexpected alliances in the past.
Obviously, Naruto himself is the main character as he is the one sent back in time. Sasuke is also often involved as Naruto's relationship with him is a central part of the Naruto story. Kakashi could be involved too, as Naruto might seek his help or try to influence his training methods. Also, the various Hokages might be important characters as Naruto could interact with them in the past to change the course of events.
One common theme is self - discovery. When Percy is sent back in time, he often has to re - evaluate who he is without all the experiences he had in his original timeline. Another theme is the butterfly effect. His actions in the past can have huge consequences for the future. For example, a small decision he makes might change the entire course of a battle.
His water - based powers might be affected in different ways. If he goes back to a time when the oceans were less polluted, the purity of the water could make his powers stronger. However, if he goes to a time when the gods were more in control of the elements, they might be able to limit his power. For example, Poseidon might have more say over how Percy can use water powers if they are in the same time period.
One interesting plot idea could be Percy going back in time to the era of the Greek heroes. He could meet Hercules and learn from him. Maybe he would have to face the same challenges Hercules did, but with his own modern - day skills and knowledge. Another idea is that he goes back to the time when the gods first emerged and gets involved in the power struggles among them. This could change the entire course of mythology as we know it.
If Percy Jackson is sent to Tartarus in fanfiction, it could be a harrowing experience. First off, the environment itself is a nightmare. The terrain is dangerous and full of pits and lava. Percy would have to rely on his wits as much as his strength. Since Tartarus is the prison for the most powerful Titans and monsters, he'd be up against foes far more powerful than he's used to. He might even discover some long - lost secrets about his powers or his family's past while trying to find a way out.
One common theme is self - discovery. Since Harry is sent back in time, he gets a chance to see his past self and the world in a new light, which often leads to him learning more about his true nature. For example, in some fanfics, he realizes his hidden strengths or weaknesses. Another theme is the alteration of the timeline. His presence in the past can change small or large aspects of the future he came from, and the fanfics usually explore the consequences of these changes.
One popular fanfic in this vein is 'Time's Twist for Harry's Bottom'. It explores the unique concept of Harry being sent back in time due to a magical mishap involving his bottom (in a rather comical way). Another one could be 'Back in Time, Bottom First' which has an interesting plot where Harry has to deal with the changes in the past while his bottom - being the source of the time - travel has some strange side - effects.
Percy might run into his old friends' ancestors. This could create some really strange and exciting interactions. For instance, if he meets an ancestor of Annabeth, he could learn things about her family history that she doesn't even know.