Well, obviously Merlin and Arthur are the main characters. Merlin is the one whose secret as a Dragonlord is revealed, and Arthur is the one who discovers this secret.
One interesting plotline could be Arthur's initial shock and then his gradual acceptance of Merlin's new identity. He might start to see Merlin in a whole new light and realize how much power Merlin truly holds.
One possible secret could be that Merlin is a powerful sorcerer from an ancient and powerful magical lineage. Maybe his family has a long - standing connection to Camelot that has been kept hidden.
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.
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.
For Merlin, there are both good and bad consequences. On the bad side, some of the more traditional and anti - magic people in Camelot might try to oppose him. However, since Arthur now knows, he has a powerful ally. Arthur can protect Merlin from those who would do him harm. Also, Merlin can now be more open about using his magic for the good of Camelot, which is a positive change.
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.
One popular plot is that Arthur is initially shocked and angry when he discovers Merlin's magic, but then he gradually realizes how Merlin has been using it to protect him all along. For example, in some fanfictions, Merlin uses his magic to save Arthur from a seemingly impossible battle, and Arthur finally comes to terms with Merlin's powers and they become even closer friends, united in a new way to protect Camelot.
Power and responsibility is a very common theme. As a dragonlord, Merlin has great power, and fanfictions often explore how he deals with the responsibility that comes with it.
The relationship could become more equal. Before, Merlin was in a somewhat subservient position, but with his magic out in the open, he becomes more of an equal to Arthur. They can now fight side - by - side in a different way, with Merlin using his magic to complement Arthur's skills. This new dynamic can add a whole new layer of depth to their relationship.