Disclaimer: I don't own Kingdom Hearts.
Inconceivable
The last thing Sora had expected was exactly what had just happened. The entire world was water, just one big ocean. He began to panic, knowing he couldn't breathe in water, and could hardly see the sun from where he was, deep under the waves. If there was any land, it wasn't for miles, because there was no sight of anything breaking the surface.
Acting on instinct he moved to go towards the light the sky the sun the air, to reach for the surf, but found himself only flailing, locked in a struggle with his limbs. Looking down at his legs…he didn't have any.
Sora's abdomen melted smoothly into a shark tail, no thighs, claves, or even toes. Instead he had fins. Still struggling, and feeling himself sinking from not being able to move against the water, Sora didn't notice the figures approaching until there was a hand on his shoulder.
"Hey, are you okay?"
Sora looked over at who had spoken, and suddenly stopped reaching for the light. Not only was he stuck within the ocean-- an entire world of water --with a shark tail, but a mermaid was talking to him. For the first time, Sora forgot that he couldn't breathe underwater, and sucked the water straight into his lungs. A split second later he was shocked to discover it was just as simple and painless as breathing air.
The mermaid giggled. He probably would have realized how silly he looked to her, marveling over something so first-nature as breathing, but he was still distracted: mermaids could giggle! He had never known that before.
"You… can't swim, can you?" She asked, kindly. "Here, I'll give you a hand." She swiftly moved from in front of him to behind him, giving him tips and telling him what to do from all directions. Sora blushed as her heard her voice from right next to his ear.
With coaching he had understood how to move about in the water, from watching her and doing as she said, from feeling and trying and getting the hang of it. He had gotten better at controlling his direction, and concentrated less on the swimming now, and more on this mysterious stranger. She was like nothing he had ever seen, a powerful but graceful tail glimmering in the moving light, and a way of swimming through the water as if she was always dancing, effortless twirls and beautiful spins as if it was nothing but a flick of her wrist. Never sitting still, but never ever fidgeting.
"By the way," she said, seeming a little silly, but still smiling that bright smile, "I'm Ariel."
Sora nodded, still simply watching her. "Sora."
"You're pretty quick-study, Sora. I think you can really handle the ocean now. Want to practice? Just follow me!" She was a yard away in an instant, having just been a blur of fluid, elegant motion. Sora smiled lightly. He'd gladly follow her.