The theme of sacrifice is quite common. Stefan was often put in situations where he had to sacrifice something for Katherine or vice versa. Fanfictions will expand on this, showing different scenarios where they make sacrifices for their relationship. Another theme is the exploration of their dark sides. Both Katherine and Stefan had their dark elements, and fanfictions will dig deeper into these, like how Katherine's dark past influences her actions towards Stefan and how Stefan's own inner demons interact with his feelings for Katherine.
One common theme is redemption. Many fanfictions explore the idea of Katherine seeking redemption and how Stefan might be a part of that journey. Another is the theme of love and obsession. Their relationship was so complex in the show, and fanfictions often play with this idea, showing how their love or obsession for each other can change over time.
A common theme is the struggle for power. Since both are strong - willed characters, many fanfictions explore who is more powerful or how they vie for power in different situations.
One common theme is the clash of different vampire cultures. Since Stefan has his own vampire lore and the Twilight series has its own, seeing how they interact is often explored.
Love and sacrifice are common themes. Often, one of them has to sacrifice something for the other, like Stefan might sacrifice his safety to protect Caroline. It shows the depth of their love.
A theme that frequently shows up is redemption. Klaus, being a complex and often villainous character, may be on a path to redemption in some fanfictions, with Stefan either helping or hindering. Also, power dynamics play a role. Klaus is very powerful, and Stefan has his own set of abilities, so how they interact in terms of power is a common theme. For example, in some stories, Stefan has to find ways to level the playing field when dealing with Klaus.
One common theme is the idea of eternal love. Since they are in a supernatural world, their love is often depicted as something that can transcend time and death. For example, in many fanfictions, even if one of them is in danger or seemingly lost, their love remains unwavering.
One common theme is friendship. Stefan and Bonnie often start as friends in the fanfictions. For example, they might be friends first and then face challenges that make their bond stronger.
One possible plot twist could be that the baby has a special power that neither Stefan nor Katherine expected. This power could attract unwanted attention from other supernatural beings, causing a whole new set of problems for them to deal with.
Another theme is power struggle. Since both Elena and Katherine have their own strengths and agendas, a lot of fanfictions play around with who has the upper hand in different situations. For example, in some stories, it might be about Katherine trying to outwit Elena in a battle of wits. And in others, it could be Elena using her newfound powers to stand up to Katherine.
One common theme is love triangles. Since it involves Damon, Stefan and an OC, often there's a complex love situation. For example, the OC might be attracted to both brothers in different ways.
One common theme is loyalty. Their status as mates often means they have to be loyal to each other no matter what challenges they face, like in many fanfics where other vampires try to break their bond. Another theme is sacrifice. They might sacrifice their own desires or safety for the sake of their mate.