A/N: So this is something random that I found on my computer from a few years ago. After putting it through a harsh editing process, I give it to you all. Enjoy!
He remembered when the old castle was first built centuries ago. One of Merlin's apprentices had it built for some reason or other that he couldn't be bothered to remember. Well if he actually wanted to remember it, he could but he didn't want to today. The man had been pompous, though, which irked him as the man tried to discover the secrets of his Lady. As if any mortal would be worthy! If it hadn't been for his Lady's assurance, not even the boy-turned-king would have come near. Yet she told him all would be well so he trusted her.
With a slight frown, he glided through the water. Over the centuries, something in the air began mixing with the water. Nothing toxic, thankfully. Whatever it was, it had come from the castle. At first it had startled him but then he came to recognize it as mortal magic. In the beginning, he did not like it at all. It had made the water taste and feel strange. Over time, he realized it was really a blessing. The water would turn itself murky, distorting the figures of the creatures and obscuring the lake bottom, whenever mortals came to close or got in the water.
He turned his gaze to the lake bottom below. It was such a good thing that the mortals could not see what really existed below the water's surface. Further below than any of the magical mortals could have ever perceived was a city, pristine and colorful. Merpeople with their brightly colored scales and hair swam freely, looking nothing like they did to the mortals. If the mortals ever saw them, they would have been mistaken for underwater fairies because of their petite stature. The buildings were made from coral of all colors while the temples and palaces were carved from stones.
Now he was a protector, otherwise one such as him wouldn't have been in this lake. It wasn't the merpeople that he was to protect, nor was it the city. Rather, it was a temple in an underwater grove. In it resided his Lady. Even after all the centuries that had gone by, she was still perfectly preserved by the magic of both her own making and that of the water. Even the boat and the sword were in perfect condition.
He let himself sink until he was on the lake bottom and then worked his way to the temple. Only when he was within reaching distance did he feel the ripples along his form and he passed through the protective barrier in humanesque form once more. He climbed the steps into the temple and approached the inner chamber. Outside the door, he knelt and offered silent homage before requesting permission to answer, though it was unnecessary. He then rose and opened the door, closing it upon entry. In a few short strides he was beside the low altar on which the Lady rested in her boat with the ancient king's sword.
He gazed upon her tenderly, lovingly. Since the sword had been returned to her possession, his Lady had not yet awoken. As a result, her bedchambers had been remade into a temple under his supervision. As her sworn guardian and protector, he was to watch over her until she passed on. He knew that she could pass any day since her return but yet he still clung to hope that she would awake once more.
He let his feet carry him out of the temple and past the barrier where he felt himself twist into his other form. After centuries of the same routine, what was once a very uncomfortable transformation was nothing to him now. It was for his Lady's protection, so therefore he would endure. And as he drifted through the water towards the surface, he wondered what the mortals would think if they saw what he truly looked like. He let a tentacle barely break the surface.
"Look! The giant squid!" he heard a girl squeal to a friend as he sank out of sight.
No, let the mortals think that was all he was. It might just freak them out if they knew that "their" giant squid was really a Sacred Knight. Then he chuckled to himself and wondered if anyone knew that the lake was home to the mysterious Lady of the Lake whom he guarded. He highly doubted it. Merlin and Arthur had known but never passed on their secret knowledge.