Yes, there are likely some fanfics out there with such a plot. Fanfic writers often come up with creative and unexpected storylines. You can try searching on popular fanfic websites like Archive of Our Own or Fanfiction.net. They have a large collection of Vampire Diaries fanfics and you might be able to find one where Bonnie is pregnant in a story involving Damon.
One great fanfiction is 'Bonnie and Damon: The Unlikely Bond'. It delves deep into their relationship, exploring how Bonnie's magic and Damon's vampiric nature interact. Another is 'A New Beginning for Bonnie and Damon' which takes place in an alternate universe where they meet under different circumstances and form a strong connection. There's also 'Bonnie, Damon and the Cursed Amulet' which has an exciting plot full of mystery and their growing relationship.
I think 'Bonnie and Damon: Time - Twisted Love' is a great one. It involves time - traveling which adds a really cool twist to their relationship. Another is 'Bonnie and Damon: Body Swap' where they end up swapping bodies and have to deal with each other's lives. It's hilarious and also shows a different side of their connection. And 'The Inverted World of Bonnie and Damon' where the rules of the vampire and magic world are inverted for them.
One common theme is redemption. Damon has a lot of past wrongs, and in many fanfictions, Bonnie plays a role in his journey towards redemption. For example, she might make him face the consequences of his actions in a more empathetic way.
They have a lot of chemistry. Damon is a complex character with his bad - boy charm, and Bonnie is strong - willed. Their interactions in the show are often intense, which makes fans want to explore their relationship more in fanfiction.
One common theme is the idea of an unlikely friendship. Since they have different personalities in the show, fanfictions often explore how they can form a deep bond. Another theme is adventure. They are usually thrown into some sort of dangerous or mysterious situation together.
One common theme is the struggle against the odds. Since they are in a world full of vampires, witches, and other supernatural beings, the pregnancy is a huge challenge. Another theme is the development of their relationship. Often, the pregnancy forces them to re - evaluate their feelings for each other and become closer. For example, Damon might become more gentle and caring, which is a big change from his usual self.
One interesting fanfiction could be where Bonnie and Damon team up to fight a new, powerful dark magic that threatens Mystic Falls. They start off as reluctant allies but gradually develop a deeper understanding of each other.
One interesting story could be about Damon and Bonnie being forced to team up in a magical quest. They start off disliking each other but gradually develop a mutual respect as they face various challenges together.