At first, Arthur would likely be shocked and maybe a bit angry or defensive. He has always seen Merlin as a friend and servant. But as time goes on, he might start to realize that he has feelings for Merlin too. Their relationship would shift from a traditional master - servant one to a more equal and passionate relationship. They would have to deal with the social norms of Camelot and how others would view their relationship, which could either bring them closer together as they face the challenges or cause some strain.
It would become much more complex. They might start off being confused and a bit awkward around each other. But then, as they start to explore their feelings, they could become closer in a more intimate way. Their friendship would be transformed into something deeper, with a new level of understanding and trust.
The relationship would be in a state of upheaval. Merlin kissing Arthur would shatter the normalcy of their interactions. Arthur might feel betrayed in a way at first because he didn't expect such a thing from Merlin. However, Merlin's kiss could also open Arthur's eyes to a side of his relationship with Merlin that he hadn't considered. They would have to communicate more openly about their feelings, which is new for them. This could lead to a more profound bond, but also there would be many obstacles in their way, like the expectations of Arthur's father, the court, and the people of Camelot.
Merlin might become even more protective of Arthur. Since Gwen is carrying Arthur's child, Merlin would see it as his duty to safeguard the future of Camelot. He could be more involved in Arthur's personal affairs, which might initially annoy Arthur but eventually he'd come to appreciate Merlin's concern.
In this type of fanfiction, it could start with Merlin having a prophetic dream where he sees himself kissing Arthur instead of Gwen. This dream haunts him and makes him realize his deeper, unacknowledged feelings for Arthur. As he tries to avoid this fate, circumstances keep pushing them together. Eventually, during a magical incident where emotions are heightened, Merlin accidentally kisses Arthur. This sets off a chain of events where they have to face the reactions of their friends and the court, and also explore their own feelings which they had previously buried deep inside.
Merlin can impact their relationship positively. He might use his magic to create opportunities for them to be alone, like creating a private garden for their dates.
Fanfiction often explores their relationship in many ways. For example, it can show how Merlin acts as a mediator between Arthur and Gwen. He might use his magic subtly to bring them closer or resolve misunderstandings. Sometimes, it shows how Arthur's sense of duty as king affects his relationship with Gwen, and how Merlin helps him balance that with his personal feelings.
During the time of Merlin's captivity, they could have long conversations that they never had before. Arthur might open up about his insecurities regarding magic and his kingdom, and Merlin could share his true feelings about serving Arthur. This would strengthen their bond in a new and unexpected way.
It could start with a slow realization of their feelings. Maybe they were friends for a long time and then suddenly, one day, they look at each other in a new light. After getting married, they become more protective of each other. Arthur might become more open to Merlin's magic, and Merlin would be more involved in Arthur's political decisions.
Some fanfictions show Arthur becoming more dependent on Merlin's magic in certain situations. For instance, when facing a powerful enemy that can't be defeated by normal means. This changes the dynamic from just a king - servant relationship to more of a partnership. Merlin, on the other hand, might feel more confident in using his magic openly around Arthur, which also alters their interactions. They could have more equal conversations and decision - making processes.
They could start by having more heart - to - heart conversations. For example, Arthur could share his insecurities about being a king and Merlin could talk about his fears regarding his magic. This would deepen their bond.
It would likely become very strained. Arthur has been brought up to uphold his father's anti - magic stance. So, when Uther discovers Merlin's magic, Arthur might initially feel betrayed and distance himself from Merlin.
The physical closeness of Merlin sitting on Arthur's lap can be the start of a deeper emotional connection. Arthur might become more aware of Merlin's vulnerability, which could lead to him being more open and caring towards Merlin in general. For example, he could start sharing his own insecurities with Merlin.