The exploration of identity is also common. Merlin may question who he is while being a slave. Is he still the same person with the same destiny? How does being a slave change his view of himself and his role in Camelot? These are the kinds of questions that are often explored in such fanfictions.
Well, power and control are major themes. Morgana's control over Merlin as a slave sets up a situation where power is constantly being negotiated. Also, themes of redemption can be present. Maybe Morgana realizes the wrongness of her actions and tries to make amends. And there's often a theme of secrecy too. Merlin might have to keep his true self and his magic a secret while being a slave, which adds to the tension.
One common theme is redemption. Morgana, in the role of a slave, often has a chance at redemption through her relationship with Merlin. Another theme is power struggle. Since Morgana has been in a position of power before, her new status as a slave creates an interesting power dynamic with Merlin.
There could be a theme of social hierarchy. In a world like that of Merlin, there are clear hierarchies, and having Morgan as a slave would really highlight the differences in status. Also, a theme of friendship or loyalty could emerge. For example, how Merlin might react to Morgan's situation and whether their relationship would be affected by this new dynamic. It could also explore the theme of identity. Morgan's identity as a slave might conflict with her true self or her potential in the story.
One common theme is the clash of different magical systems. Merlin has his druidic magic and Loki has his Asgardian magic, so a lot of fanfics explore how these two types of magic interact. For example, in some stories, they might try to combine their powers to defeat a common enemy.
In sub Merlin fanfiction, a major theme is secrecy. Given Merlin's sub position, he must keep his magic a secret, and this secrecy drives a lot of the plot. Another theme is growth. He grows as a person and as a magic - user while being in a sub role. It's about how he overcomes the limitations of his position. Additionally, the theme of sacrifice is common. Merlin is often in situations where, because of his sub role, he has to sacrifice something for the greater good, whether it's his own safety or his relationships.
The theme of sacrifice is also quite prevalent. In many fanfictions, Merlin's father has made sacrifices for Merlin's future, which Merlin discovers as the story progresses. It gives a deeper understanding of their relationship.
In Merlin vampire fanfiction, the theme of acceptance is quite common. Whether it's Merlin accepting the existence of vampires or the vampires accepting Merlin's power. Another is the theme of transformation. Merlin might transform in some way due to his encounters with vampires, or the vampires themselves may transform, either physically or in their attitudes. And the theme of forbidden knowledge often pops up, as the vampires may possess knowledge that is both dangerous and alluring to Merlin.
Another theme is friendship. The neckerchief can be a focal point for the relationships Merlin has with Arthur, Gwen, and the other characters. For example, it might be a gift from a friend that holds special meaning.
Another theme is self - discovery. When Merlin crossdresses, he often discovers new aspects of himself or how others perceive him differently. For instance, he might learn that he can be more confident in a different guise. Also, it can be about breaking gender norms. In these fanfictions, Merlin challenges the traditional gender roles of the Camelot society, which adds an interesting layer to the story.
One common theme is the shock and disbelief among the characters. Given Merlin is male in the original series, his pregnancy is quite unexpected, so characters often struggle to come to terms with it.