Love and passion are common themes. Since it's lemon fanfiction, there is often a strong focus on the physical aspect of their relationship as well as the emotional connection.
Another theme is self - discovery. Through their relationship, both Bonnie and Damon often go through a journey of understanding themselves better. Their love makes them face their own insecurities, fears, and desires in a way that they might not have without each other.
Another theme is the power of friendship turning into love. They start as friends or reluctant allies and then slowly develop deeper feelings. This is seen in a lot of fanfics where they initially work together against a common foe and then realize they have more than just a friendly connection.
A prevalent theme is redemption. Damon may be portrayed as a character who needs to redeem himself in Bonnie's eyes, or through his love for Bonnie, he finds a path to redemption. Also, the theme of forbidden love often shows up. Given their relationship's nature and the context of the original story, it can be seen as something that goes against the norm, which adds an exciting and often angst - filled aspect to the fanfiction. There's also the theme of mutual growth. Their relationship can be a catalyst for both of them to grow as characters.
Well, a frequent theme is the change in their relationship. The pregnancy can either bring them closer or cause some initial friction. Also, the theme of secrecy sometimes comes up. They might want to keep the pregnancy a secret from their enemies or some of their more judgmental friends. And there's always the theme of preparing for the future, like finding a safe place to raise the child.
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.
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.
Love is a very common theme. Since they are in a human context, their love is more about normal human connections, without the supernatural elements influencing it directly.
One common theme is love triangle. Since Bonnie, Damon and Stefan are all connected in the Vampire Diaries universe, the love triangle between them is often explored. It creates a lot of drama and tension.
Love and passion are very common themes. Since it's often about Damon, there's usually a strong sense of attraction and a complex relationship. For example, in many of these fanfictions, the OC might be initially hesitant about getting involved with Damon because of his reputation, but then they can't resist the pull towards each other.
One common theme is the idea of a forbidden or unexpected love. Since Bella and Damon are from different fictional universes, their relationship is something that goes against the norm in their respective stories.
One common theme could be friendship. Despite their differences, they might develop a strong bond. Another could be adventure, where they go on some sort of journey together.