The baby could have a really interesting relationship with Klaus. Since Elijah is Klaus's brother, Klaus might be both protective and a bit jealous of the baby. He could see it as a new addition to the family that he needs to look out for, but also as someone who might take away some of the attention from him.
Well, it could have super strength. Since Elijah is a powerful vampire and Elena has her own special traits from being a doppelganger, their baby might inherit enhanced physical abilities. Maybe it could move at super - speed like vampires do, but also have some kind of mental power from Elena's side, like being able to sense danger in a different way than normal vampires.
Love is a very common theme. Their relationship, whether it's a budding romance or a deep platonic love, is often explored. Another theme is the idea of sacrifice. Given the complex situations they are often in, one or both may have to sacrifice something for the other.
Another possible reason is the need for comfort. Elena has been through a lot in the supernatural world. Elijah, with his calm and collected demeanor, could offer her a sense of safety. A kiss might be a way for them to find solace in each other, especially in a fanfiction where emotions are heightened and the characters are constantly dealing with life - threatening situations.
One common antagonist could be Klaus. He has his own motives and often clashes with Elijah. His presence can create a lot of tension between Elijah and Elena as well, since he might target Elena to get to Elijah or vice versa.
Elena's friends and family might be a bit wary at first. After all, Elijah is from a different world. Her aunt Jenna might be concerned about the implications of this marriage for Elena's future. However, her friends like Bonnie and Caroline could come around once they see how much Elijah loves Elena. For Elijah's family, some might be happy to see him find love, while others, who are more traditional or power - hungry, might see Elena as an outsider and try to break them up.
In this fanfiction, Elena's family may initially be shocked, but then quickly come around to support her. They could start making plans for the baby's future, like setting up a safe place to live. Elijah's family might have a more complex reaction. The elders might see the pregnancy as a sign of change in the family's power structure. Some younger members could be excited and look forward to having a new family member, while the more conservative ones may be skeptical and try to interfere in the pregnancy for their own reasons.
One great 'elijah elena fanfiction' could be 'Elijah and Elena's Unlikely Bond'. It focuses on how their different personalities interact in a really interesting way. It shows Elijah's calm and collected nature against Elena's more impulsive side, and how they grow to understand and support each other throughout various challenges in their fictional world.
The Salvatores would probably be shocked. Damon might be initially angry, thinking Elijah has taken advantage of Elena. Stefan, on the other hand, would be more concerned about Elena's well - being and the implications of a half - vampire, half - something - else baby. He'd want to make sure she's safe.
One interesting storyline could be Elijah protecting Elena from other powerful vampires. Since Elijah has a sense of honor, he might see it as his duty to keep her safe.