Their relationship could develop through shared danger. For example, if they are both targeted by a powerful witch in New Orleans. They would have to rely on each other for survival, and this mutual dependence might lead to a grudging respect. Then, over time, that respect could turn into something more like friendship or even a deeper attraction.
Perhaps Elena is sent to New Orleans by her friends to seek a cure for a new vampire - related ailment. Klaus, who still has an interest in Elena, offers his help but on his own terms. They end up in a power struggle within the vampire community of New Orleans. As they interact more, Elena starts to see a different side of Klaus, a side that is not just the cruel and power - hungry vampire she thought he was. This new perspective makes her question her own feelings towards him.
One great Klaus and Elena fanfiction is 'The Bond Beyond Blood'. It explores a unique relationship between them where they have to team up against a common enemy. The story is filled with intense emotions and some great character development for both of them.
She could be terrified at first. After all, Klaus is a very powerful and dangerous vampire. But Elena is also a strong - willed character. So she might quickly gather her courage and start looking for ways to escape.
One challenge could be the safety of the baby. Given Klaus's complex past and the many enemies he has made, there might be threats to the baby's life. Also, Elena, who was once a normal girl turned vampire, has to adjust to the new role of a mother in a supernatural world. They might also face challenges in terms of the baby's identity, whether it will be more vampire or more human in nature.
The main reason is the chemistry. In the show, there was always this underlying tension between Klaus and Elena. Fanfiction writers can explore that in more depth, like how their relationship could have developed if certain events had been different. It gives fans a chance to see a different side of their dynamic.
One common theme is the struggle against the judgment of others. Since Klaus has a rather dark past in the supernatural world, many fanfictions show how Elena and Klaus deal with the disapproval of their friends and family regarding their marriage.
Another theme is loyalty and betrayal. Given their complex relationships and the world they live in, there are often situations where loyalty is tested. For example, Elijah's loyalty to Klaus might be put to the test because of his feelings for Elena. And vice versa, Klaus might feel betrayed if Elijah gets too close to Elena.
I'm not sure if there is a specifically highly recommended 'Klaus and Elena make love' fanfiction. Fanfiction can vary greatly in quality and content. You might want to check on popular fanfiction websites like Archive of Our Own and search for such stories. However, it's important to note that some fanfictions may not adhere to the original spirit of the characters or may have content that not everyone will be comfortable with.
The other vampires in Mystic Falls who are against the idea of a hybrid - vampire baby could be antagonists. They might see it as a threat to their way of life.