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.
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.
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.
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 popular 'yandere arthur x merlin fanfiction' is 'The Obsessed King'. In this story, Arthur's yandere tendencies start to show when he realizes his deep feelings for Merlin. He becomes overly possessive, which creates a lot of tension and interesting plot twists. The author does a great job of portraying Arthur's internal struggle between his love and his controlling nature.
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 is the exploration of gender roles. Since it's a male pregnancy, it challenges the traditional ideas of male and female roles. Another theme is the deepening of the relationship between Merlin and Arthur. The pregnancy often serves as a catalyst for them to become closer and more reliant on each other.
One common theme is loyalty. Since they are brothers, their loyalty to each other is often a central focus. They will go to great lengths to protect one another.
Love, in different forms, is a recurring theme. It could be platonic love that is so strong it's like a family bond. Or it could be a romantic love that the authors explore in a very subtle or sometimes more obvious way. This love is often what drives them to make sacrifices for each other in the fanfiction stories.