Another theme is changing the past or future. Sometimes Elena tries to fix things that went wrong in the past or prevent bad things from happening in the future. This can lead to some really complex and interesting storylines as she grapples with the consequences of her actions.
I've read 'Elena Through the Ages of Time Travel'. In this fanfiction, Elena's time travel is not just about going to the past but also to different possible futures. It's full of mystery and exploration as she tries to figure out how to get back to her original timeline while also learning important lessons about her own life.
I really liked a fanfic where Elena and Kol time travel to the Middle Ages. It's a bit of a different take as they have to navigate the social norms of that time while also dealing with their own feelings. There are some really intense and romantic scenes in it. It shows how their characters develop in a new and challenging environment.
It might also become more complicated. If they travel to a time when one of them was in love with someone else, like when Elena was still with Stefan in the past, it could create jealousy and confusion. They would have to face these emotions and decide if their current relationship is worth fighting for.
A cool plot might be that Elijah discovers a time - traveling device. He uses it and accidentally brings Elena with him to different points in time. In the process, they see key moments in the history of their families and the supernatural world. Along the way, they realize that their fates are more intertwined than they thought, and they have to work together to put things right in the timelines they've disrupted. Maybe they also fall in love during these adventures across time.
There could be a popular one where Elena and Caroline time travel to the era of the Originals when they were first turned. They get involved in the power struggles of that time and have to use their wits to survive. This would be full of political intrigue and action, which many fans might find appealing.
The theme of power struggle often comes up. Kol is an original vampire with a lot of power, and Elena has her own agency. When they time travel, they might face situations where their powers are tested or they have to work together to gain power in a certain time period. This creates a lot of tension and interesting plot twists in the fanfiction.
One idea could be that Elena and Elijah travel back to a time when their families had a different relationship. They could try to change the course of history to prevent some of the tragedies that happened to their families. For example, they might stop a feud that led to a lot of bloodshed.
Fanfiction.net is also a good place to start. It has a vast collection of fan-written stories. Look for the relevant categories or use the search bar. Sometimes, you might need to dig a bit deeper by browsing through different sections related to the show they are from to find the time travel stories about Elena and Elijah.
One idea could be that they travel back to a time when the founding families first made the deal with the vampires. They could try to change the terms to prevent all the future chaos. Another could be traveling to a time when they first met, but with their current knowledge and feelings, and seeing how that alters their relationship from the start.