Love, in different forms, is also a theme. It could be platonic love with a possessive edge, or it could be budding romantic love. The fanfiction may explore how this love affects their actions and decisions. For example, Arthur's possessive actions might be his way of expressing love without fully realizing it. And Merlin's reaction to it can be a way to show the growth of their relationship.
Love and protection are common themes. Arthur's possessiveness often comes from his love for Merlin and his desire to protect him from harm. For example, in many fanfics, Arthur will not allow others to harm or even insult Merlin.
One aspect of 'possessive arthur x merlin fanfiction' could be the exploration of Arthur's possessive nature in relation to Merlin. It might show how Arthur is overprotective or territorial about Merlin. This could stem from their deep friendship and the importance Merlin has in Arthur's life, like in battles where Arthur always wants Merlin by his side and gets a bit possessive if others try to take Merlin's attention away from their mission.
Love and obsession is also a major theme. The line between Arthur's love for Merlin and his obsessive yandere behavior is often blurred. The fanfictions usually explore how Merlin responds to this love - turned - obsession. Sometimes Merlin is confused, other times he tries to understand and help Arthur deal with his extreme emotions.
One common theme is the exploration of a new kind of relationship. With Merlin being pregnant, it changes the power dynamic and the way they interact. Another theme is acceptance, both from themselves and from the people around them.
Another theme is the forbidden love aspect. Given their different roles in society, their relationship might be seen as unacceptable in the context of the story's world. This adds a layer of drama and tension. Some stories also focus on how they overcome these societal barriers. Moreover, magic is usually a big part of it, as Merlin is a powerful magic user. His magic can either be a source of conflict or a way to bring them closer together.
One common theme is friendship. Their relationship is often at the heart of the stories, showing how they support and grow with each other. Another is loyalty. Arthur and Merlin are extremely loyal to each other in the original series, and this is often emphasized in fanfiction.
One common theme is the exploration of gender roles. Since Merlin is female in these fanfics, it often challenges the traditional gender roles in the Arthurian legend. For example, how a female Merlin would be perceived as a sorcerer in a male - dominated society like Camelot.
One common theme is the struggle with unspoken love. Arthur's jealousy often arises from his love for Merlin that he can't or won't admit. It's a way of showing his possessiveness in a romantic sense without being fully aware of it himself.
One common theme could be loyalty. Merlin is often extremely loyal to Arthur, and when he breaks a rule, Arthur's punishment might be a test of that loyalty. Another theme could be power dynamics. Since Arthur is the king and Merlin has magic which is often a secret, the punishment could be related to maintaining the balance of power in Camelot.
Another theme is the test of their relationship. The hotel can be a place full of challenges and temptations. It could be other people trying to come between them or some difficult situations that make them question their loyalty to each other. Like in some fanfictions, a powerful sorceress at the hotel tries to charm Arthur away from Merlin, but they overcome it and their relationship becomes stronger.