One idea could be Madara traveling back to the era of the Sage of Six Paths. He could try to change the very foundation of ninjutsu, which would create a whole new timeline. Maybe he would attempt to gain the power of the Sage for himself much earlier in history.
Madara could time travel to a key moment in his own past, like right before he made a certain fateful decision. He might then be able to prevent his own downfall. For example, if he had not made the deal with Kaguya in his original timeline, he could rewrite his entire future and the future of the ninja world.
One interesting plot twist could be that female Naruto, with her knowledge of the future, tries to prevent Madara from making certain mistakes that led to his downfall in the original timeline. For example, she might show him the true nature of the power he was seeking, making him question his motives.
Perhaps the fanfiction could center on the unborn child's potential power. Madara might worry about the child being used as a weapon or a tool by his enemies. There could also be a side plot about the reactions of the other ninja clans when they find out about Madara's pregnancy, and how it might change the power dynamics in the ninja world.
In some narusasu time travel fanfiction, Naruto might go back to the time when Orochimaru was first targeting Sasuke. He could then use his skills and knowledge to keep Sasuke safe and away from Orochimaru's influence. A different plot could be Sasuke traveling to a time when Naruto was ostracized as a child and being the one to support Naruto, which would change their relationship dynamic from the start. Also, they could travel to a time during a major battle and use their combined future knowledge to turn the tides in their favor.
One plot idea could be Naruino traveling back in time to prevent a great disaster in their world. Maybe a powerful enemy once defeated them in the past, and by going back, they can change the outcome. Another could be traveling to the future to see how their actions in the present have affected the world. For example, they might find that their current choices led to a utopia or a dystopia.
One plot idea could be Arya traveling back in time to the days before her family's downfall. She could use her knowledge and skills to prevent certain events from happening. For example, she might stop Ned Stark from making some of the political missteps that led to his execution. Another idea is Arya traveling to the future of Westeros. She could see the long - term consequences of the power struggles she was part of and try to change things in her own time. Maybe she'd witness a new dynasty rising or a great war that she could try to avert.
Maybe Chuck travels to the future and discovers that his actions in the present have led to a dystopian world. He then has to go back and make different choices to avoid that future. This could involve complex character development as he grapples with the knowledge of what might be.
Well, Anakin might time travel to a crucial moment in the Galactic Republic's history, like the Trade Federation's blockade of Naboo. He could use his skills and future knowledge to prevent the events that led to so much chaos. He could also travel to a time where he meets his future children as a stranger and has to figure out how to interact with them without revealing his true identity, all while trying to change the course of his own dark future.
One idea could be a character going back in time to prevent a major villain's origin. For example, if someone went back to stop All for One from corrupting Tomura Shigaraki as a child. Another plot could involve a hero traveling to the future to see the outcome of their current actions and then coming back to make changes. Maybe a student like Izuku Midoriya goes to a future where the heroes have lost and tries to change the present to avoid that fate.
A time - traveling dragonborn could be sent back to the era when dragons first arrived in Skyrim. They would have to use their dragonborn powers in a different context, maybe even having to learn new ways to control their abilities. They could also try to change the relationship between dragons and humans from the very beginning.
A great plot could be that the ace in the fanfiction discovers a time-traveling device by accident. They then use it to travel to different historical events. They might end up changing something small in the past that has a huge impact on their present world. For instance, they could accidentally prevent an important scientific discovery from happening in the past. Now they have to travel through time again to fix what they've broken. This creates a lot of suspense and adventure.