One possible plot could be Future Trunks traveling back in time to prevent a new threat that he discovers in his own time. For example, a powerful and unknown enemy is about to emerge in his future, and he goes back to enlist the help of Goku and the others before it's too late. Another plot could involve Trunks accidentally changing something in the past that has unforeseen consequences in his future, like messing with the timeline of a certain character's power - up, which then leads to a whole new set of challenges when he returns to his own time.
He becomes more resourceful. In his own time, he's used to a certain set of circumstances. But during time travel, he has to adapt quickly to new situations and find ways to use the resources available in the past. For example, he might have to figure out how to use different senzu beans or power - up techniques that are new to him.
A lot of Trunks' time travel fanfiction focuses on fixing the past. He has the power to change things that went wrong in the original timeline. It's really cool to see how writers use this concept to create alternate versions of the Dragon Ball story.
One possible plot could be Naruto using the Rinnegan's time - travel ability to prevent the Uchiha massacre. He could change the course of history and save Sasuke from a life of revenge.
One possible plot could be that Android 18 and Goku time travel to the past to prevent the Androids from ever being created. They might face challenges like dealing with the Red Ribbon Army before they start the Android project. Another plot could be that they travel to a future where the Earth is in ruins and they have to find a way to change the events that led to it. They could also time travel to an alternate timeline where Goku was never sent to Earth and see how that changes everything.
One possible plot could be Hermione using her knowledge to help the Marauders in some way. For example, she might assist them in dealing with a difficult spell or situation that they were struggling with in their original time. Another plot could be her trying to change certain events that she knows will have negative consequences in the future, but then facing the moral dilemma of interfering with time.
One interesting plot could be Future Trunks arriving in a new timeline where lemons have some sort of magical power. He has to figure out how to deal with this new element while also protecting the timeline from threats. Another plot might involve Future Trunks having an encounter with a character who is obsessed with lemons, and their strange relationship leads to various adventures. And there could be a plot where Future Trunks uses lemons as a symbol to inspire hope in a dark and desolate future, like using lemon - scented items to remind people of better times.
One idea could be Future Trunks bringing back a technology from the future that changes the course of the present timeline's battles. For example, a more advanced scouter that can detect hidden power levels more accurately.
One possible plot could be that Harry travels back in time to Tom Riddle's school days at Hogwarts. He could try to prevent Riddle from turning into Voldemort by befriending him and showing him a different path. Maybe Harry uses his knowledge of the future to expose the dark magic that was influencing Riddle at the time.
One possible plot could be that James, Lily, and Albus travel back in time to the Marauder's era. They could interact with the young versions of their family members, like Sirius and Remus. Maybe they try to change some small events to prevent future tragedies without messing up the timeline too much.
Another plot could involve them traveling to a different timeline altogether. In this new timeline, they might find themselves in a world where the power of Geass doesn't exist. This would force them to rely on their wits and leadership skills in a completely different way. They could either try to find a way back to their original timeline or decide to make the best of the situation and change this new world for the better.