One idea could be Naruto going back in time and preventing the Uchiha massacre. He could use his knowledge of future events to change things for the better in the Uchiha clan, and this would also have a huge impact on Sasuke's character development.
In a 'Percy back in time fanfic', Percy could travel back to the time of the Titans' rule. He would be in a world full of chaos and oppression. Maybe he teams up with some of the early heroes who were fighting against the Titans secretly. He could learn new powers or fighting techniques from that era. His presence there could also cause some of the Titans to be more cautious, which could potentially change the outcome of the Titan - god war. This would then have a huge impact on the present that he came from, as the world would be very different in terms of power dynamics and relationships between different mythological beings.
One idea could be Naruto going back to the time when the Uchiha clan was still intact. He could try to prevent the massacre by changing certain events or by influencing key people. Another plot could be him traveling back to his own childhood and using his future knowledge to become an even more powerful ninja earlier, like learning advanced jutsus much sooner.
One idea could be Naruto going back in time and preventing the Uchiha massacre. He could use his knowledge of future events to stop Itachi from having to make that tragic choice.
Maybe Percy travels back to the founding of Camp Half - Blood. He could meet the first demigods and see how the camp was established. He could also learn ancient fighting techniques and bring them back to his time to use against modern enemies. This would add a really cool element of anachronism to the story.
Another plot could be that Hermione goes back in time and ends up changing the relationships between the main characters. Maybe she accidentally causes a rift between Harry and Ron, and then has to figure out how to fix it while also dealing with the overarching threat of Voldemort in that time period.
One idea could be exploring how Naruto has mastered new jutsu during the time skip. For example, he might have developed a unique combination of his Rasengan and Sage Mode techniques. Another plot could focus on the relationships that have changed. Maybe Sakura has become a more independent and powerful kunoichi, and there are new tensions or reconciliations within Team 7.
One idea could be exploring how the future technology in 2015 from the fanfic affects the daily lives of the characters more deeply. For example, how do the flying cars impact traffic rules and social interactions? Another could be a new character introduced in the fanfic who has a special ability related to the time - travel technology and how that changes the story's dynamic. Maybe this character can manipulate time in a different way than the original characters, leading to new adventures and challenges.
One idea could be that the time travel orb sends Naruto to a crucial point in the past where he can prevent a major tragedy. For example, he might be able to stop the Uchiha massacre, which would change the entire future of the ninja world. This would lead to different alliances and power dynamics.
Maybe in the time loop, Naruto accidentally switches bodies with Sasuke during a crucial battle. This leads to a series of humorous misunderstandings as they try to navigate each other's lives and relationships while still in the middle of the fight. For example, Sasuke - in Naruto's body - might accidentally flirt with Sakura in his usual stoic way, which just confuses everyone.
A possible plot could be that in the 'naruto time travel academy fanfic', Naruto goes back and discovers a hidden conspiracy within the academy that was overlooked in the original timeline. He then teams up with his younger self (sort of a mind -meld situation) and some of his friends to expose the conspiracy and save the academy from an unseen threat. This would involve a lot of sneaking around, using his future knowledge of the academy's layout and the people in it.