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.
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.
One plot idea could be the challenges they face in keeping the pregnancy a secret from their enemies. Another could be how they prepare for the arrival of the baby in a world filled with supernatural threats. For example, they might have to find a safe place away from the constant power struggles in their supernatural community.
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.
One interesting plot twist could be that the pregnancy is a result of a magical spell gone wrong. Maybe a witch with a grudge against Elena cast a spell that made her pregnant with Elijah's child against their will. This would add a lot of drama as they have to figure out how to reverse it while also dealing with the reactions of their friends and family.
Another plot could involve Elena dealing with a family crisis. For example, a family member gets sick and she has to take on more responsibilities while also taking care of herself, day by day. She could learn about the importance of family and self - care during this process.
Well, in 'Elena goes back in time fanfiction', she could go back to a time of a great war. Maybe she tries to use her modern knowledge to end the war early. She could also go back to a time when there were ancient artifacts that hold great power, and she has to find them before someone else does in the past, so that in the present, those artifacts don't fall into the wrong hands. This would involve a lot of adventure and mystery as she navigates the past world.
One common plotline is how they deal with the reactions of their families and friends. Since their relationship might be unexpected, it can create a lot of drama. For example, Elena's friends from her original circle might be skeptical or even hostile at first.
One idea could be that Elijah tries to court Elena in a very old - fashioned and gentlemanly way. He might take her on trips to historical places he has known over the centuries, sharing his stories and knowledge with her. This would be a contrast to the other vampires' more aggressive approaches towards Elena.
A really interesting plot could be that Elena and Mateo get transported to a different realm. In this realm, their powers work differently and they have to learn how to adapt and work together to find a way back home. They meet new allies and enemies in this strange new world and their relationship deepens as they rely on each other for survival.
A possible plot could be that Bella and Elijah are from different species in the fanfiction world, for example, one is a vampire and the other a werewolf (assuming such a scenario exists in this fanfic). Their pregnancy is then a very unique situation that defies the norms of their world. This could lead to a lot of drama, with different factions either trying to protect or harm them because of the baby. They would have to rely on each other and a few trusted friends to navigate this new and dangerous situation.