Oh God, I COULD DO SO MANY THINGS WITH THIS ONE. But I'll go with the fancier version of it. Unless you want the other one as well?
For nightwalker!
Underwater Kiss I
Steve had always heard stories about mermaids. The most famous probably being Andersen's The Little Mermaid, even if the original had made him cry like a baby the first time he'd heard it. Disney's version just didn't compare, even with the happy ending.
So, yes, Steve had heard stories about mermaids. But that didn't mean he'd believed them.
Until he'd fallen off the cruise ship he'd been working on with Bucky. It was his own fault for being out there during a thunderstorm. And it was his own damn fault for seeing something in the water and thinking it was someone who'd fallen overboard. He'd gotten the lifebuoy and was going to throw it overboard when a particularly fierce of gust of wind blew him right over the railing and sent him hurtling head first into the choppy water.
All the air punched out Steve's lungs with the contact, the water too dark for him to tell which way was up to safety. Going up and hitting the ship would not be a good idea.
Lightning flashed, and Steve jerked back in shock upon seeing another person right next to him. He had dark eyes and hair, his mouth framed by a goatee. He was also looking right at Steve with an implacable expression.
Steve closed his eyes, thinking he'd been hallucinating, and was about to try and swim for the surface to get some air when he felt something grab hold of his wrists.
His lungs burned as he exhaled air that he didn't have in a surprised burst of bubbles, and his eyes snapped open, stinging in the salt water.
The other person that he'd seen was even closer now, his face mere inches from Steve's and all the clearer for it. Now Steve could see that his eyes were brown and filled with a startlingly clever intelligence.
He felt something scaly and cold slip between his legs, and his eyes drifted closed again even as he felt lips press against his own, parting them gently with a warm tongue.
That was when Steve reached his limit, and his body reflexively tried to heave in air. Steve struggled, expecting water to hit his lungs, but instead there was air - air coming from the other man's mouth as he breathed oxygen into Steve.
Clutching at the other man's arms and only vaguely surprised to feel something scaly and fin-like meet his fingers, Steve simply floated there, held tight by the strange man and letting him breathe for him, mouths pressed together.
Later, much later after Steve had been found floating on a piece of driftwood by the crew of a passing ship and Bucky had reunited with him, Steve would look out at the ocean and wonder about the strange man who had saved his life.
Because we could do with more mermaid!AUs! Also, this is a much longer tale than what I've got here, but it's just a kissing scene.