The banter between Merlin and Arthur in fanfiction is really interesting. It can range from light - hearted jabs at each other's habits. Merlin might poke fun at Arthur's love for jousting and how he always gets a bit too competitive. Arthur could retort by mentioning Merlin's clumsy attempts at serving him. Their banter also reflects the underlying respect they have for each other despite their different social standings. It's like a friendly sparring that keeps their relationship dynamic.
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.
Merlin might have used his knowledge of the castle's secret passages. He could lead Arthur through those passages, away from the assassins. Also, Merlin could have called upon some magical creatures he's befriended, like the dragon, to help him. The dragon could fly in and either scare the assassins or carry Arthur to safety.
In fanfiction, Arthur might be rough with Merlin because of a prophecy or a pre - ordained fate. He might think that by being tough on Merlin, he can prevent some bad outcome that he believes is related to Merlin. For example, if there's a prophecy that Merlin will bring great change to Camelot, Arthur might be rough in an attempt to keep things as they are, out of fear of the unknown.
I really like 'The Dragon's Prophecy' in Merlin Arthur fanfiction. It has a lot of action and adventure while still focusing on the relationship between Merlin and Arthur. It shows how Merlin's magic is tied to Arthur's fate in an exciting way. 'Merlin's Secret' is also great as it delves into the secrecy of Merlin's magic and how Arthur slowly discovers it, adding a lot of tension and drama to their relationship.
In such fanfictions, Merlin is often portrayed as a very powerful sorceress. She has an air of mystery around her. Her magic is usually depicted as extremely potent and she uses it to protect Arthur or further their shared goals. She might be shown as a manipulator at times, using her intelligence and magic to influence events in their favor.
In some versions of this type of fanfiction, Arthur's reaction is complex. He might be stunned into silence when he first finds out. His mind would be racing with thoughts about all the times Merlin has used his magic to save him or Camelot without his knowledge. After the shock subsides, he may have a heart - to - heart with Merlin. They would talk about the implications of the secret, and Arthur would likely start to view Merlin in a whole new light, as not just his servant but as a powerful ally with a great burden.