I've intentionally left this vague enough you can read it as slash or friendship, it's up to you. It just sort of ignores Series 4.
Disclaimer: I don't own Merlin, I earn nothing from this but the enjoyment of writing it (and maybe getting a few reviews, hint hint).
Their friendship had always been like a game with rules no one but them seemed to know or understand. The push and pull of their bond was one that confounded more than a few outsiders and, sometimes, even themselves.
They spent their time directing jibes and insults at one another. Mostly innocuous and never intending harm, though no blame was placed when one went too far. Retaliation was sought, accepted, and then all was forgiven. Their little wars never escalated beyond the reasonable.
The rules of the game for observers were always and, it seemed, had always been set in stone (though Merlin had only been around for less than five years, so work that one out). Few were allowed join the game, most would ever remain an observer, but there were some and every new player brought their own set of rules.
Some of the new players' rules made sense to everyone.
Some seemed as random and arbitrary as the rules Merlin and Arthur made for themselves.
Any unwelcome intrusion to their world was met with a united front. Together, they were undefeatable... Though no one could understand why Merlin was a necessity or when he had become so. It was simply an accepted fact that he was.
Arthur and Merlin.
Merlin and Arthur.
They were as much a single entity as they were individuals. Injury to one was treated as an injury to both. An insult to one was treated as an insult to the other (true insults anyway... teasing insults were met with laughter and more of the same; always happy to make fun of each other but never willing to actually hurt).
And then Merlin's magic was revealed and the whole of Camelot seemed to hold their breath. They didn't know if this broke the rules of the game, but it certainly broke the laws of the game board on which they played. They watched and waited, Arthur could not change the laws of the game board... For, though he ruled in his father's stead, Uther yet lived and only the king could change the rules so drastically.
No one was surprised when Merlin escaped the dungeon. They were even less surprised when no search party was sent to look for him. And all of Camelot grieved, because they were sure the game was over now.
But then, at the first sign of danger... There was Merlin. A strange wooden staff in his hand and an insult on his lips. And the whole of Camelot rejoiced. Because, though it seemed the rules of the game had changed, the game was not yet over. (Although, the death of the latest sorcerer set on their destruction might have had something to do with their happiness. Just a little.)
A smirk. A tease. The knights were after him but their dark haired savior was gone, the smile still brilliantly lighting up his face.
And so the game didn't end, it merely moved on to the next level.
And it became an unspoken expectation of the knights that they would have his aide. (Unspoken only because if they expected him to be there, they would be expected to make plans for his capture). And if, on the occasions Merlin was injured, Arthur and his knights seemed to run a little slower when chasing after him... Well, they were weighed down by armor and heavy swords while he carried only the clothes on his back and his staff.
… And he'd once been a servant so he knew all the hidden pathways the knights didn't.
… And things always seemed to trip them when they chased him.
… And they could never seem to agree which direction he went (which usually developed into in-depth discussions as to the benefits of which direction would be better that could last anywhere from several minutes to over an hour).
So they couldn't really be blamed if he managed to outrun them, could they?
That is not to say they never captured the young man, but his capture always seemed as much a part of the game as his escapes and he was always gone by morning. And, on the occasions they caught him because he was too injured to escape on his own, if Arthur was heard to tell Gaius Anything he needs, just keep him alive,then no one commented.
Neither did they comment when Arthur would take sporadic hunting trips alone and return without even rabbit to show for it. And if these trips tended to last a bit longer or be a bit more frequent after Merlin was injured... Well, that could only be coincidence, couldn't it?
And then Arthur became king.
And, though some grieved the death of Uther, all rejoiced for the coronation of his son.
And they waited with baited breath...
Because the rules were about to change once more.