The towels you and Lydia had wrapped around yourselves to dry off are quickly cast aside as you kiss and fondle, enjoying each others naked human bodies. After quite a bit of this, you are quite erect. You roll over so you are on top of Lydia and slide into her. You and Lydia quickly establish a rhythm as you ride the waves of passion. As much as you are enjoying Lydia's human form, the thought of her as a mermaid crosses your mind. It's like you can't get that fantasy completely out of your head.
Lydia occasionally lets out a soft moan and each time she does her legs seem to shift. After enough of this, you start to wonder if something is happening and slow down only to have Lydia insist you continue. You oblige and quicken the pace, soon bringing you both to a grand climax.
Lydia lets out a ecstatic scream as you finish, something she has never done before. You certainly aren't that good! As you collapse in exhaustion, you feel something touch your feet that doesn't feel quite right. Laying down on the bed next to Lydia you notice she has a dreamy expression on her face. You gaze follows down her body from her head down to her toes...except she no longer has toes. Instead, Lydia's legs have formed themselves into a tail again, this time without a swimsuit or water. Unlike the scales of a classic fishtail or Lydia's previous spandex tails from her swimsuits, Lydia's latest tail looks like her normal skin. But the shape is unmistakable: Lydia is a mermaid again!
You remember that at one point during sex you thought of Lydia as a mermaid. Is this your fault? Until now, the effects of your wish seemed to have taken on a certain structure. Lydia's eyes began to flutter.
"Lydia, you're not going to believe this..."