Perhaps in the fanfiction, Caroline's pregnancy makes her a target. There could be an ancient prophecy about her unborn child that some of the villains in The Originals want to use for their own gain. So she has to go into hiding and rely on the help of some unexpected allies. This would lead to a lot of action -filled scenes as they try to protect her and the baby from the bad guys.
A possible plot is that Hayley discovers some unique powers or prophecies related to her unborn baby during her pregnancy. This could lead her on a journey to find out more about the baby's destiny. Also, the pregnancy could be used as a way to bring different factions in the 'The Originals' world together, either in support or against her.
One idea could be that they face opposition from their respective families or vampire/werewolf communities. Their pregnancy might be seen as a threat to the status quo or an abomination in the eyes of some. Another plot could involve them trying to find a safe place to raise their child, away from all the danger and politics. Maybe they go into hiding in a remote location and have to learn to live a normal life while also dealing with the challenges of Caroline's pregnancy as a vampire.
One idea could be that Klaus and Caroline are forced to face their relationship when they find out about the pregnancy. They might have to deal with the reactions of their families and friends. Another could be that Caroline tries to keep it a secret at first, but Klaus discovers it and they then have to figure out how to move forward together. There could also be a plot where an enemy tries to use the pregnancy against them.
One plot idea could be that Klaus and Caroline try to keep the pregnancy a secret from their enemies. They might go into hiding in a remote place, like a small cottage in the woods. There, they would face challenges of living a normal life while Caroline is pregnant. Klaus, who is used to a life of power and danger, would have to adapt to being a more domesticated partner, getting firewood and protecting their new home. Another idea is that the pregnancy causes a rift between their friends and families. Some might see it as a threat or a bad union, while they fight to prove that their love and the new life they are bringing into the world is a positive thing.
One idea could be that Caroline's pregnancy is a result of a magical mishap. Maybe a spell gone wrong in Mystic Falls. The baby could have special powers, like being able to sense vampires from a distance. This would bring a whole new set of challenges for Caroline and her friends as they try to protect the baby from the various threats in the vampire - filled world.
Perhaps in the fanfiction, Caroline is pregnant in a world where there are magical or supernatural elements. She could be pregnant with a special child that has unique powers, and she has to protect it from those who might want to use its power for evil.
I'm not sure specifically as it could vary greatly. It might be a fan - made story where Caroline, perhaps from 'The Vampire Diaries' or related universe, takes actions to save the characters from 'The Originals'.
Another plot could involve Caroline's werewolf friend Tyler coming back and being initially skeptical but then becoming a strong support for them during the pregnancy. This could add some drama as there are historical tensions between vampires and werewolves.
Perhaps a plot where Hayley discovers something unique about her pregnancy that is related to the werewolf or vampire lore in the show. For example, her unborn child could have powers that start manifesting while still in the womb, and she has to figure out how to handle this new development.
A fanfic on Caroline being pregnant could start with the moment she discovers she's expecting. It could then explore her emotions - from shock and fear at first to gradually accepting and even looking forward to motherhood. The story could also involve her preparing for the baby, like decorating the nursery and buying baby clothes.