This started as a rough drabble and is not slowly getting a plotline, but it's slow going. I've started this story on ao3 fanfic site about 4 years ago and today finally uploaded a new chapter, so I thought why not put it up here too.
Hope you enjoy and please review.

It was at that moment that they realized just how powerful Merlin truly was.

They'd known of his magic for a time now, long enough to grow comfortable in its presence. Though it still awed them on almost every single encounter -be it something as simple as starting a fire or something as lethal as sending a sword flying through the air aiming straight at the opponents' heart- Merlin's magic was a part of them now, just as much as Merlin was, for he was no mere servant to any of them. First and foremost, he was their friend.

So no, they were not surprised at Merlin's capable magic nor his eagerness to face danger to protect everyone else. Merlin had told them and showed them what he could do, ranging from simple spells to powerful enchantments and dangerous magics.

Merlin could makes objects float or change shape to be something else entirely -he could control swords and other weapons to fly straight at his opponent or break tree branches as thick as Arthur's head and make them fall on enemies heads. He could conjure fire to threaten and invoke fear or simply to light the dark. He could even control the very heavens and call down lightning upon whomever was stupid enough to cross him.

But Merlin did neither of those things this time. One moment a raging inferno came crashing through the air burning everything in its path and beyond, hellbent on reaching them, engulfing them, destroying them. And Merlin, he simply pushed his way to the front of the group and raised his right hand towards the fire and just as Arthur regained enough sense to realize Merlin's dying predicament -the fool, always sacrificing himself- the fire reached his hand.

Arthur froze, dread filling his body, his mind listening to the agonizing screams of his best friend writhing as the flames engulfed and burned his body- but none of that happened.

Arthur watched in stunned disbelieve -and from the gasps around him he gathered his knights weren't fairing much better- as the raging fire seemed to collide with Merlin's hand as if slamming into a tremendous wall. The flames parted, smoothing to either side and bursting in the new direction it was forced. An almost golden air surrounded them, not so much air as appearing like something solid, like armor only in a gigantic sphere around them.

Merlin was shielding them!

As Arthur watched closer, he saw a fierce determination in Merlin's eyes that he couldn't help but feel proud of. No matter how much magic Merlin had showed him, no matter how much Merlin surprised him day in and day out, no matter what... Merlin never ceased to inspire awe in him.

Suddenly the feeling of awe was quickly crushed as a tremendously strong wave of pure energy -for it could be nothing else- slammed into Arthur and the knights and they found themselves flying backwards, literally, feet of the ground, body thrown through the air and landing in a painful heap quite a distance away.

Despite the pain, Arthur struggled, upwards creaking limbs and all, as panic settled into his stomach. For he knew that magic, felt its desire to protect. Another one of Merlins' quirks, his emotions were so tied to his magic or perhaps the other way around, that those affected by his magic could sometimes feel whatever Merlin was feeling at that time.

Merlin has pushed them back just now, thrown them back and for Merlin to cause harm, any harm to either of them meant that they were in serious danger. Arthur could barely see Merlin as the fire that so eagerly spread away earlier, suddenly encircled him. The golden shield shimmered oddly as if it were growing dimmer.

It was failing! Merlin couldn't hold the shield, the unslaught must be too great.

The dread from earlier revisited Arthurs' stomach, the screams reverberating through his head, pounding on his skull... only this time, this time they weren't imagined.

"MERLIN!"