You make out with your girlfriend, your tails entwined and hands roaming over each other's bodies.
"Let me show you how amazing it is being a mermaid" Amy whispers then moves down to your new chest. She uses her mouth on your nipples and you can't believe how sensitive they are now. The change to a female body has you feeling all sorts of new pleasurable sensations. It's all so much you have a small first orgasm.
Amy feels your body shake and kisses you deeply. "The first of many" she assures you. She looks at the confines of the tub and realizes there's not enough space for what she has in mind. She climbs over the side of the tub and flops onto the wet tile floor. You follow, a bit awkwardly since your mermaid body is so unfamiliar.
"There's something I've always fantasized about doing and now I can..." says Amy before gently pushes you onto your back. She kisses her way down your body and you realize what she has in mind. You feel her hands reach under and grab your butt then feel something warm and wet slide into something you've never had before. Your tail wants to start thrashing around, but Amy is laying on top of it as she pleasures you.