Well, she sure liked having her tits touched, so...
I stopped massaging 'em and she opened her eyes and looked into mine. I thought about how to indicate what I wanted. I tried shifting my legs and laying down next to her, then patting the wet sand under her back to try to get her to imitate. She got the gist and obliged, and we laid on our sides and looked at each other for a second. Then I sat up, motioning her to stay down. She watched intently. I slowly swung a leg over her and maneuvered above her chest, positioning my dick between her tits. She looked with wide eyes as I squeezed her bosom together and started slowly fucking it. She made a super high-pitched noise that must've meant she liked it, because she didn't stop me.
I decided maybe I had died and gone to Heaven after all, it was just an oddly sea-themed Heaven appropriate for my watery death. My dick sliding between those wet, salty mountains of marshmallow was a pleasure beyond life and death, beyond Heaven and Hell, and as I sped up she clawed at the sand with her webbed hands, and a couple times her tail gave a hard slap against the ground, splattering wet sand onto my back. Her face contorted wildly and the sounds she made were all over the map of clicks, whistles, and squeals.
I felt myself going over the edge, and I didn't know what she'd think of my cum, so I pulled out, stood up, stepped to the side, and furiously jacked myself off into the sea while staring down at her glistening half-human body. Spurts of cum blasted feet from my dick and impacted the water, making little splashing noises. She watched me with interest, and when I collapsed onto my ass and removed my hand to steady myself, she slid over and stuck her head down, peering at my cock. She watched it slowly shrink, still giving the occasional twitch. I breathed heavily; I'd never come so hard from a titty fuck, even though it was my favorite sexual activity! Or, hell, activity of any kind.
I was tired, of course, and I stretched out backwards on the sand, closing my eyes. I heard the mermaid slide up next to me, and opened my eyes back up to find her looking at me with some concern. I smiled to reassure her, and she smiled back uncertainly. She returned to looking at my cock, apparently confused by its change in size.
I closed my eyes again, but I shortly felt her webbed hand pinching at my member. I kept the smile on my face, and she kept poking and pinching, trying to provoke a reaction. Then she wrapped her whole hand around my limp cock. Well, she just saw me do it, so she must get the gist. She squeezed a bit hard and I flinched, looking up; she eased up, eyeing me, and I smiled again. She tried to stroke my cock slowly, but it was too small and soft. I laid back and looked at the sky while she continued working.
It took a few minutes, but before long she had my cock waking up. Noticing the change, she increased her efforts. I looked up and watched her tits jiggle as she jerked me, and in no time I was steely again. It was just a shame she lacked the proper sheath for my sword.
I suddenly realized I'd fucked--or half fucked--this woman--or half woman--but I hadn't kissed her yet. How would she feel about a kiss? I reached my hand up to her neck (she stopped jerking me off for the time being), and for the first time I noticed she had gill slits in it. Moving above them and to the bottom of her jaw, I held her head and smiled at her again. She smiled back, again. I slowly moved our faces together, and she went with it, eyes locked on mine. Our lips touched, and she didn't seem to know what to do, so I gave her a demonstration. Unsurprisingly, her mouth tasted very salty, but her tongue and teeth seemed perfectly human. I wrapped my arms around her back and she followed suit, and we embraced for several minutes as I further educated her in the art of kissing.
We parted, and it occurred to me that kissing might be a good lead-in to giving head. I splashed my hand in the tide to wash the sand off and then inserted a finger into my mouth, to try to plant the idea. She mimicked me, but found it harder because of her webbing. Carefully, I inserted my own finger in her mouth, hoping she wouldn't bite down. She didn't, but she seemed puzzled. I slid my finger back and forth a couple times, then pulled it out and scooted back a little. I pointed down to my cock, and after a second, she got the idea and took it into her mouth. She slid her body backwards into the water and laid down on her tits, sucking and bobbing in my lap. She didn't know what she was doing, but it felt good nevertheless. I enjoyed her ministrations for a while, and she kept her eyes tilted up at me, apparently eager to give me pleasure.
Her mouth was extra-wet and felt wonderful, but as I looked down at the backside of her body, I noticed something I'd missed before. I slid my fingers into her hair and gently pulled up, indicating to her to stop; my cock popped out of her mouth and she looked up questioningly. I leaned down over her back and inspected her scaly tail. Reaching down with both hands, I took hold of the tail and parted a telling fold, revealing a very human-looking anus.
I'd only had anal with one girl before, who was crazy for it--she suggested it. But I knew a lot of girls didn't like it. With the mermaid, though, everything was foreign to both of us, and she seemed to trust me to show her new means of pleasure...
Well, if she didn't like it, I'd stop. But I had to try it. She didn't have a pussy, but she had an ass. In fact, the more I looked at it, the more the top-back of her tail looked like a firm pair of lady buttocks--just covered with scales.
I walked on my knees into the surf behind her with her looking back to watch me. I swung a leg over her tail and reached down with both hands, taking hold of what I now thought of as her thighs. I pulled upward, and she arranged herself into the equivalent of a four-legged position, with the remainder of her tail going between my legs. I smiled and she returned it.
I dipped my hand in the water and slid my finger up her tail, over her asscheek, and in toward her anus. She seemed to enjoy the sensation. I pushed in a bit, and her eyes widened. I stopped, and she looked at me blankly. I started again. Working slowly, I got my finger all the way in, and she still looked mostly blank, as though she didn't know if she found this pleasant or not. I removed my finger and splashed some water over her ass, which made her smile and squeak. Applying more water, I slowly worked a second finger in. This time she made some clicking noises, which I hoped meant she was starting to enjoy the feeling.
As my fingers came out I realized how hard my cock was, and decided I couldn't wait any longer. I grabbed it and guided it to the hole, and at last she seemed to understand what I was going for. I squeezed myself in, and god was it tight! Tighter than any pussy, and when I was all the way in she contracted a little to become even tighter than Sonia's ass (the other girl I mentioned, obviously).
It felt like a human ass, only wet, almost like a pussy. The tide seemed to be coming in around us too, and I started pulling out and then sliding back in with the rhythm of the waves. She undulated her ass side to side, now clearly taking pleasure in the feeling. A wave crashed against my own ass and I thrusted hard into her, pulling her back toward me from the thighs. She squealed loudly and pulled forward, then thrusted back at me. I knew she was liking it, and now I couldn't hold back.
I started fucking her faster, and she pushed right back into me, whistling and screeching in delight. I sped up until I was pounding her at the pace of a train, and the waves broke dramatically over our interspecies fuckfest. Slowing for a moment to catch my breath, I reached down and grabbed both of her wrists, pulling her arms back and shoving myself into her ass; she threw her head back and let out a piercing wail that cut through the air, and I fucked her sweet mermaid ass as fast and hard as I could. Behind me, her tail slapped my own ass, egging me on like a bull. She leaned her head all the way back to look into my eyes, and I could see her enormous tits flopping all over the place as my furious thrusts wracked her half-human body. After another spanking from her tail I let go of her wrists and she fell forward; I seized her thighs and frantically fucked the hell out of her until, without warning, the orgasm hit, and for a moment the world disappeared and there was nothing but blinding white pleasure.
Falling back into reality, my seed exploded into her ass, and it felt like it had the force of a firehose. I shot blast after hot, salty blast until cum leaked from around my dick to be lapped up by the ocean. I collapsed onto her back and she turned her head and kissed me, and the sea churned around us as we laid there exhausted in the sand, man and mermaid united by pure sexual bliss.