Maybe the pregnancy is unexpected, and they initially panic. But then they start to get excited about building a family together. Chloe could start to train Lucifer on how to be a good father, like teaching him about baby care and normal family values, which would be a big change for him since he's from Hell.
Another plot could be that there are forces in the supernatural world that either want to harm the unborn child or use it for their own purposes. So, Chloe and Lucifer have to team up with their friends, like Mazikeen and Dan, to protect their baby. This would involve a lot of action and drama as they fight off various threats.
One idea could be that they struggle to balance their work with the upcoming baby. For example, Lucifer's devil - related duties and Chloe's police work. Another could be that they have different ideas about how to raise the child, given their very different backgrounds. Maybe Lucifer wants to raise the child with a more 'devil - may - care' attitude while Chloe is all about discipline and rules.
One idea could be that they face challenges in their relationship due to the pregnancy. Maybe Lucifer is worried about his devilish nature affecting the baby, while Chloe is trying to balance her detective work with the new situation. Another plot could involve them having to protect the unborn child from supernatural threats, as Lucifer's world is full of such things.
One idea could be that the baby has some sort of special power. Maybe it can see things that others can't, like angels or demons in their true forms. This would add an interesting dynamic as Lucifer and Chloe try to understand and protect their child from the otherworldly forces that might be interested in the baby's power.
One common plot idea is how they deal with the challenges of having a baby while Lucifer is still adjusting to his life on Earth. For example, he might be worried about his devilish nature affecting the baby in some way.
One idea could be that they face challenges in their relationship due to the unexpected pregnancy. For example, Oliver might worry about how his vigilante life could affect the baby and Chloe. Another could be that they go on a journey to find a safe place for their family, away from the threats in Smallville. They could also have to deal with the reactions of their friends and family, some of whom might not be as supportive as they hoped.
One common theme is the exploration of their relationship dynamics when they are about to become parents. It often shows how they support each other during the pregnancy.
The fanfiction could also be about the challenges Chloe faces during her pregnancy. For example, she might have health problems during the pregnancy. She could also face social issues, like dealing with people who judge her for being pregnant at a certain age or in a certain situation. The story could show how she overcomes these difficulties and grows as a person.
In some fanfictions, Lucifer could kidnap Chloe as part of a plan to prove a point. For example, he might be trying to show her how vulnerable she is without his protection. This could lead to a series of events where Chloe discovers new aspects of Lucifer's world and her own place in it.
One interesting plot could be their adjustment to married life while still dealing with the supernatural elements in Lucifer's world. For example, how they handle his devilish powers and the reactions of those around them.
One potential antagonist could be Lucifer's father. He might not approve of the union or the baby, seeing it as a disruption to his grand plans or as something that could change Lucifer in a way he doesn't want. Another could be some of the demons from Hell who see the baby as a potential threat to their power or existence if it has some sort of unique abilities.