Another theme is the change in relationships. His friends, like Arthur, Gwaine etc., might react in different ways when they find out or suspect. Some may be supportive, while others might be initially shocked or confused. For example, in many fanfictions, Arthur has to come to terms with his best friend being pregnant, which is a big shift in their dynamic.
One common theme is secrecy. Since Merlin's situation is so unique and perhaps not fully understood in the context of Camelot, he often has to keep his pregnancy a secret, which creates a lot of tension in the stories.
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.
One common theme is the challenges she faces. Since Merlin is usually depicted as a powerful figure in the Merlin universe, being pregnant might limit her abilities in some ways, and this can create a lot of internal and external conflicts. For example, she might have to hide her pregnancy from certain characters who could pose a threat.
One common theme could be the struggle between her magical duties and the pregnancy. Since Merlin has important magical tasks, being pregnant might create a conflict.
One big theme is the exploration of magic. In many Merlin female fanfictions, the female characters are either learning magic, or have a special connection to magic that is different from the male characters. For instance, a female character might have a more intuitive approach to magic. Also, the theme of friendship is present. A female character could form a strong friendship with Merlin or other characters like Guinevere, and this friendship is crucial in their adventures.
Power and responsibility are common themes. As Merlin becomes king, he has to handle the power he's gained while being responsible for his kingdom. Another theme is magic and its role in ruling. Since Merlin is a powerful sorcerer, fanfictions often explore how his magic affects his kingship, whether it's for protection or for the betterment of the kingdom.
One common theme is the loss of hope. As Camelot collapses, the characters often struggle with losing their faith in the future. Another theme is the test of loyalty. Friends may turn against each other in the face of chaos.
Another theme is the empowerment of female characters. In these fanfictions, the female characters usually break free from the traditional roles and show great strength and independence, especially in the context of their relationships.
A prevalent theme is the exploration of magic itself. How the magic in the Harry Potter universe and that in the Merlin universe are related or different. Also, destiny plays a role. Fanfictions often explore how their destinies are intertwined, whether it was meant to be that they meet and change the course of events in both their worlds.
One of the main themes is the conflict between Merlin's secret magic and the public perception in the royal court. There's also the theme of destiny. Merlin is often seen as having a great destiny in relation to the royalty. And love, whether it be platonic or romantic between Merlin and the royal characters, is a frequent theme. For example, in many fanfictions, Merlin forms a deep bond of friendship with Arthur that is almost like a brotherly love. His loyalty to Arthur and the kingdom is constantly tested by his need to hide his magic.
Magic is a very common theme. Since it's about Merlin's ritual, magic is at the core. It often shows how powerful Merlin's magic was through the ritual.