The eternal suffering

DIR (2): A fish without a tail

Arthur must be the biggest idiot in the world, if he thought he could swim while wearing armor.
Merlin was already thinking up new insults and curses, as he dived deeper and deeper into the ocean.
It was cold. Cold and freezing. His movements only warmed him a little. But the cold pressed on his lungs and begged for his mercy.

It reminded him that his oxygen supply was limited and he couldn't waste it by thinking too much. So, instead, his only thought, the very focus of his mind was:
Get Arthur to safety.

But as Arthur was wearing armor, he was dragged down faster than Merlin could swim. Merlin's eyes were wide, burning from the salt water, as he could see Arthur drift further and further away.
And he knew, if he swam back up to get air, he would loose every chance of getting Arthur back for good.

Arthur's eyes were wide open, as he recognized Merlin above him. None of his movements to get to him and stop himself from sinking, helped him. If anything, they just exhausted his energy and precious oxygen.
Compared to the storm, it was eerily silent under water. Everything was muffled and the pressure from sinking lower pressed on their ears. Here and there they could hear objects being thrown into the water far far above them.
That was all they heard. And they couldn't scream or call out. They could only hold their breath and hope they'd manage to reach each other in time.

Merlin was getting desperate. He couldn't reach Arthur. Arthur was sinking much faster than he could swim. And it didn't take long until Arthur gave up trying to swim upwards. The weight of his armor restricted his movements, exhausted him faster. His eyes went glassy, and he began sinking motionlessly. Even faster than before. He had exhausted his resources.
Merlin panicked. And panic is not good when you're under water and can't breathe. There is a reason why people hyperventilate when panicked. Your brain needs oxygen. Air. Neither of which was around them.
Still, Merlin didn't even get the idea to swim back up. It was far too late anyway.

In a split decision, he magicked the straps and belts open that held Arthur's armor together. And he forced it to fall off.
He didn't even care that Excalibur sank down with it. You could blame him for not doing this sooner. But the entire situation took maybe a minute. Thinking up useful solution takes time sometimes. Especially, when your mind is occupied with thousands of ideas how this could end. Each idea worse and more terrifying than the last.

Now Arthur was without his armor. And the sinking slowed. But that didn't give him back his oxygen. And Merlin was already exhausted too.
His vision started to swim. No pun intended.
He barely managed to reach Arthur. But he did. All he could do was grab him tight and heave him upwards in one desperate motion. One kick of his legs. That was all he could do. All his energy had left for him.

Somewhere in his mind, he could only pray that this wasn't what destiny had planned for them. For Emrys and the once and future king.

The surface was too far up. And at this point, Merlin couldn't even tell were up actually was. Chances were he got them even deeper. And the water, roused by the storm, was dragging them both far away from the ship. His orientation was completely lost.
Merlin lost consciousness. The last thing he felt, was a magical presence close to them.

Whatever it was, it pulled at his arms. It grabbed both him and Arthur. But that was all he could remember.

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Merlin and Arthur coughed out what felt like liters of water. But of course, it couldn't be as much. Because if their lungs were full of water, they'd be dead.
Heaving and rasping, they took in the salty air. Unable to see anything at first.