One popular one is 'The Once and Future King' fanfic series. In this, Merlin often uses the term'sire' as he plays his role as Arthur's advisor. Another is 'Camelot's Heart' where the relationship between Merlin and Arthur is very much in line with the traditional Arthurian tales, and Merlin's use of'sire' is quite prominent.
In Merlin fanfiction, Merlin calls Arthur sire as a sign of respect. In the Arthurian legend and related fictional settings, sire is a term used to address a nobleman or a person of higher status. Merlin, being Arthur's servant and advisor in many versions, uses this term to show his loyalty and deference to Arthur's position as king or prince.
I'm not sure about the most popular ones specifically. But you can start by looking on major fanfiction platforms like Archive of Our Own. There might be stories where the author takes a creative turn and has Arthur in a situation that seems like cheating on Merlin in their own fictional take on the relationship, often exploring complex emotions and consequences.
One popular 'Merlin Saves Arthur' fanfiction might be 'The Saving Grace' where Merlin uses his magic in a really creative way to rescue Arthur from a powerful dark sorcerer. It's full of action and shows the deep bond between them.
Some fanfictions focus on the theme of alternate universes. In these, the Merlin - Arthur kiss can happen in a completely different setting. For instance, they could be in a modern - day world where they meet in a different way than in the original story. Or perhaps they are in a world where magic is accepted openly, and their relationship develops more freely. This allows for creative interpretations of their relationship and the significance of their kiss.
One popular theme is unrequited love. Arthur might want Merlin but be unable to express it due to his status or other obligations. Another theme could be the discovery of Merlin's magic and how that affects Arthur's feelings towards him.
These fanfictions also play on the idea of the underdog being protected. Merlin often hides his true power and is in a vulnerable position in Camelot. Arthur, as the king or prince, has the power to shield him. It creates a dynamic that fans find very appealing. For example, in many fanfictions, Merlin might be targeted by dark magic users, and Arthur's role in saving him is exciting to read.
One great fanfiction could be 'The Enchanted Bond' where female Merlin uses her magic in unique ways to protect Arthur. It has a really interesting take on their relationship and the challenges they face in a world that fears magic.
One great 'Arthur Protects Merlin' fanfiction is 'The Protector's Oath'. In this story, Arthur discovers a plot against Merlin and immediately takes steps to safeguard him. He assigns extra guards to Merlin without revealing the true reason, all while being his usual gruff but caring self.
In some fanfictions, Arthur saves Merlin from a magical creature that has been sent specifically to target Merlin because of his powerful magic. For example, a dark wizard sends a shadow demon after Merlin, and Arthur, with his courage and swordsmanship, manages to slay the demon and save Merlin. This often leads to a deeper bond between them as they realize how much they mean to each other.
One interesting Arthur courts Merlin fanfiction could be one where Arthur discovers Merlin's magic in a very unique way, like during a battle when Merlin has to use his powers openly to save Arthur. This creates a whole new dynamic between them as Arthur has to grapple with his long - held beliefs about magic and his friendship with Merlin.