One possible plot could be that they initially struggle to adapt to parenthood. Bonnie might be worried about how her magic could affect the baby, and Damon would be overprotective. They could face challenges from the vampire and witch communities, but their love for each other and the baby would help them overcome difficulties.
In this fanfiction, it could start with an unexpected pregnancy. Bonnie and Damon are shocked at first but then gradually embrace the idea of having a child. As the baby grows, they discover that it has an uncanny connection to the supernatural world around them. They seek the help of their friends, like Elena and Stefan, who may have mixed reactions. But through it all, Bonnie and Damon's relationship deepens as they become parents and face the joys and terrors of raising a supernatural baby together.
Well, perhaps in the fanfiction, the baby has some sort of special power. Since Bonnie is a witch and Damon is a vampire, the baby might inherit a unique combination of abilities. This could lead to other characters either trying to protect the baby or wanting to use it for their own gain. Bonnie and Damon would then have to fight to keep their family safe.
Well, at first, they might be a bit clumsy in their new roles as parents. Damon, who is used to being a bit of a loner, would have to open up more to Bonnie and the baby. Bonnie would be more in control in some ways, as she would use her witch knowledge to take care of the baby. Their relationship would shift from just being a couple in love to a family unit, with all the added responsibilities and deeper emotional bonds that come with it.
Well, perhaps the story could revolve around how their relationship changes with the new addition. They might struggle to balance their love for each other and their newfound parental responsibilities. For example, Damon's wild side might need to be tamed a bit more as he becomes a father, and Elena has to deal with the stress of being a mother in a world full of danger.
One interesting story could be about how Bonnie and Damon's baby has special powers due to their unique heritages. The baby might be able to control magic in a way that surprises both of them.
One possible plot could be that they face many challenges in raising the baby. Maybe there are threats from the supernatural world that target their child. Damon, with his protective nature, would be on high alert all the time, while Elena uses her compassion to raise the baby in a loving environment.
Perhaps there's a plot twist where Damon doesn't initially believe the baby is his and it causes a rift between him and Bonnie. Or, the pregnancy could be a part of a prophecy that neither of them knew about, and fulfilling it has unforeseen consequences for the whole group of characters.
You can try fanfiction.net. It has a large collection of fanfictions including those related to Bonnie and Damon and their potential baby. There are filters you can use to narrow down your search.
One possible reason could be that Bonnie has a unique strength and independence. She's a powerful witch, and Damon might be attracted to that power. Also, Bonnie has always been there for him in tough situations, more so than Elena in some ways.
I recommend 'Bonnie and Damon: A New Beginning'. This fanfic takes a fresh look at their relationship. It starts with them in a rather hostile situation but then gradually builds up their connection in a very believable way. The character development is well - done, and it's a really engaging read.
The idea of Bonnie being pregnant for Damon in fanfiction also gives room for character development. For Bonnie, it could mean facing new responsibilities and for Damon, it might be a chance to show a more caring and committed side. Fanfic writers can take this premise and explore themes like love, family, and sacrifice within the context of this new situation.
In the fanfiction, perhaps the baby's birth is a very difficult and dangerous process. Since both Bella and Damon are from different fictional universes with their own set of rules regarding vampires and such. The baby could be a symbol of a new beginning for their relationship, forcing them to put aside their differences and work together to protect their child. They may have to face challenges from both the vampire and human communities who are either afraid of or envious of the baby.