That's all the invitation you need. Seeing on actual mermaid is stunning enough, seeing six of them is beyond belief, but actually swimming with them is the kind of opportunity that you just can't pass up. You slip out of your shoes and strip down to your bra and panties and jump in. The sudden blast of cold water surrounding you cause your skin to tighten up on itself. You swim up and break the surface and gasp as your head pokes out of the water. You pant a bit and the mermaids giggle at your reaction to the water. You tread water and look back at them for a few moments before managing to catch your breath.
"Oh my God that's cold!" you say breathlessly. The mermaids giggle again, even the red and indigo colored mermaid smirks a little.
"You'll get used to it." the orange and yellow mermaid says to you "Now enough talking I thought you wanted to swim with us." You smile and nod, and with that you're off. You don't go out to far, but farther then you'd ordinarily swim. You laugh with them during brief rest periods, occasionally getting water splashed in your face. The mermaids show quite a bit of fascination with your legs, occasionally touching them or swimming through them as you tread water. You figure that it must be just as rare for them to see human legs as it is for you to see mermaids. You find it odd that that didn't occur to you. What also doesn't occur to you is how long you swim with them, not until you and they are resting on the beach and you glance over to see the very beginnings of a sunrise peak out over the horizon.
A sudden feeling of something sliding around your left leg brings your attention to the orange and yellow mermaid slipping a small anklet on your left ankle. She smiles at you as she ties the two ends together. You lift yourself up into a seated position and look at your ankle. It's a simple design, with small yellow-green and white beads alternating.
"What's this?" you ask with a smile.
"It's a gift." she says to you.
"Aww...to remember you all by?" you ask.
"I have a feeling that you won't forget us." she says. This causes a couple of the other mermaids to giggle. One of them, the teal and blue one, pulls herself closer and rests her hands on her shoulder as you lay back down.
"So...you enjoyed swimming with us?" she asks.
"Enjoyed would be an understatement." you say to her.
"I'm glad," she says with a mysterious smile "a lot of us are starting to like you."
"Well thank you-oh!" you say and look down at your right ankle. The orange and yellow mermaid is tying another anklet to your ankle.
"Another one?" you ask.
"They're a matching set." she says and crawls up between your legs and rests on you chest. You blush as she does. "You know. The sun is about to rise. We have to leave soon." You frown at her.
"Wow really?" You look at her and to the one on your right "I'm really going to miss you guys." The two mermaids resting on you are joined by a third on who rests on your left shoulder.
"When I said we, I meant you too. Hold her girls!" she says to the others. Before you can ask what's going on the other two mermaids grab on to you and hold your arms down. The yellow and orange mermaid grabs the back of your head and kisses you. She moves her hand behind your back and slips the clasp of your bra with one hand and uses some sort of sharp object to cut the side of your panties off. She then discards it and pulls you closer. One of the other mermaids pulls your underwear away. You feel a tingle after you've kissed for a while and she finally releases you.
"What are you doing?" you ask as she pulls away and leans back, giving you a mischievous look. Suddenly your ankles snap together. You look down and see that the two anklets have pulled against each other and almost look like they've merged. You try to pull your ankles apart, but they won't budge. You start to reach down to pull the anklets off but the other mermaids hold you back. Then you feel the strange feeling. The beads on the anklets are getting bigger and attaching to your skin. Whats more they're multiplying. They spread down to your feet, which become thin as the balls of your feet merge and turn outward. It hurts, but not as much as you'd have expected, and soon not at all. You watch as webs form on your toes and your feet get flatter and thinner, forming a fin.
"No...no no I can't be a mermaid." you say to them.
"Can and will." the red and indigo mermaid, who happens to have been the one that held you down on your left says "If humans ever found out about us, we'd be hunted and probably put in an aquarium and stared at.." Your face shows fear as you listen to her speak and look as the scales are spreading up your thighs and reaching across your legs to join them together. As they do your legs form into one leg and your bones and muscles shift into a mermaid's tail.
"So," the blue and teal mermaid says "We talked to each other during the swim while you were distracted. We decided that since you loved mermaids so much, that we'd turn you into one. Trust me there are much less pleasant things we could have done to ensure you kept our secret."
"I like ice cream too, that doesn't mean I want to be a bowl of it. Look I'll keep your secret I promise, just don't turn me into a mermaid. Please!" you plead with them. The all look at each other for a while, as though they're thinking. While they do, your knees snap together as the scales crawl up them. You feel them disappear under the scales. Up your knees and around your thighs the scales crawl warping your former legs into a mermaids tail. You look at them with a pleading look on your face.
"Well...there is a magic pearl that can reverse the spell, but only if the new tail hasn't been underwater." the orange and yellow one says.
"Well, where's the pearl?" you ask.
"Underwater." she says and laughs "No I'm just kidding, there is no pearl, no reversing the spell, no going back."
You can't believe what you're hearing, but try to control your breathing as the scales march between your legs, and up over your rear. Two more fins form around your waist. You glance down at yourself, as the pain subsides from your tail and fins following the change you lift your fin to look at your new tail, giving it a couple of twitches and thumping it against the sand once or twice. You look up at the mermaids, who now are all surrounding you. The emotions get the better of you and you end up crying. A few of them give you affectionate hugs to offer comfort, which helps, oddly enough. You sit there weeping until sunrise.
"Enough of this. It's time to go now." the silver and sky-blue mermaid says. With that the other mermaids help you to the beach. As your tail touches the water it tingles again. In fact your entire body tingles. You dive into the water, swimming alongside your new sisters, enjoying the water rushing past you and seeing the ocean in a way you never would have imagined. By the time you get to the place the mermaids call home, you not only know you're never going to be human again, but you don't even care to.