Another interesting plot could be the OC traveling to a time during Atem's final battles. The OC might have the power to change the course of the battle slightly, leading to different outcomes for some of the characters. For example, they could save a minor character who was supposed to die, which then has a ripple effect on the overall story.
The OC could also time travel to a time before Atem was born. They could meet Atem's ancestors and learn secrets about his family line. This knowledge could then be used when they return to Atem's time. They might discover an ancient prophecy related to Atem that no one in his time knew about, and this could play a crucial role in his future.
One idea could be an original character traveling back to the time of Aegon's Conquest. They could try to change the course of history by preventing certain alliances from forming. For example, they might stop the Starks from allying with the Targaryens, which would have huge ramifications for the future of Westeros.
Well, the OC could interact with Atem in his younger days. Since the OC has knowledge of Atem's future, they might act in a way that puzzles Atem. For example, the OC could drop hints about future events, making Atem curious and eager to know more. This creates a unique dynamic as Atem tries to figure out the OC's true nature.
Another interesting concept is if an enemy from the past is brought to the present in a time travel accident. Maybe Salem is accidentally brought forward in time. This would force the RWBY characters to face her with their current skills and knowledge, leading to intense battles and strategic planning as they figure out how to send her back or defeat her in this new time.
One idea could be that a modern Beyblader gets transported back in time to the origin of Beyblading. He could then learn the ancient techniques and bring them back to the present, revolutionizing the sport. Another idea is that a past Beyblading champion is brought to the future to see how the game has evolved. This could lead to some interesting battles and exchanges of strategies.
One idea could be Batman traveling back to the time when Gotham was first founded. He could try to prevent the seeds of corruption from being sown. Another plot could be him traveling to a future Gotham that has been completely overrun by villains and he has to find a way to change that future by altering events in the past. Or perhaps he travels to different time periods to gather knowledge and technology to better fight crime in his own time.
One idea could be a stormtrooper traveling back in time to the Clone Wars era. He could find himself in the middle of a battle and have to decide which side to support, if any. Another plot could involve time traveling to a future where the Empire has fallen and seeing how the galaxy has changed.
One interesting idea could be a character going back in time to prevent the initial titan invasion. They might use their knowledge of future events to change strategies and save more lives. For example, if Eren knew from the start how to better fight the titans, he could have trained the soldiers more effectively.
A cool plot could be that a villain from the future uses time travel to go back and change the past in order to gain ultimate power in the Arrow universe. The heroes then have to figure out a way to reverse the changes and stop the villain. This could involve a lot of action scenes as they race against time to save their world from this altered timeline.
A cool plot for a Pokemon time travel fanfic might be that a Pokemon researcher travels back in time to study ancient Pokemon species that are now extinct. Along the way, they encounter problems like not being able to use modern technology to catch or study the Pokemon. They might have to rely on the knowledge of the people in that era. Also, a trainer could travel through time to meet their ancestors who were also Pokemon trainers and learn about their family's history in the Pokemon world.
Maybe a character from the future RWBY world travels back to the time when the Huntsman academies were first founded. They could introduce new fighting techniques or ideas that were developed in their time, which would have a huge impact on how the early Hunters and Huntresses are trained.