One of the main themes is friendship. In many Merlin Holmes fanfictions, they start off as strangers or even a bit suspicious of each other, but then develop a strong bond of friendship as they work together. For example, they might learn to trust each other's skills and judgment. Also, mystery - solving is a big theme. The fanfictions often create new and exciting mysteries that require both Merlin's magic and Holmes' deductive reasoning to solve. And there's also the theme of adaptation, like how Merlin adapts to the modern - ish world of Holmes or vice versa.
A common theme is the combination of magic and detective work. Since Merlin has magic and Holmes is a detective, their stories often involve using magic to solve detective - like problems or Holmes trying to understand Merlin's magic. Another theme is the clash of two different worlds, as Merlin is from a medieval - like fantasy world and Holmes from a Victorian - era detective world.
A common theme is family. Since they are siblings, fanfictions often explore their family bond, whether it's a strained relationship at first that gradually improves, or a strong bond from the start that they rely on during cases. For example, in some stories, Sherlock initially underestimates Enola but then realizes her value as a family member and detective.
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.
Redemption is also a common theme. Since Morgana often takes a darker path in the original, many fanfictions explore the possibility of her redemption, with Merlin being a key factor in that journey. Love, in various forms, is another theme. It could be a platonic love born out of mutual understanding or a more romantic love that defies the odds.
One common theme is the clash and eventual harmony between magic and science. Since Merlin represents magic and Nobel represents science, their interactions often explore how these two different forces can coexist.