"...I've always dreamt about being a mermaid, but I never told you that those fantasies involved...being a lesbian." your girlfriend shyly reveals to you.
You start to piece the clues together, becoming a bit anxious. "But, if that's what you always dreamt, then that would mean-"
The two of you hold each other closely as the bathtub's water splashes about wildly, as your legs quickly begin to transform into a long, fishy appendage, complete with long beauitful red fins. You could only moan as the transformation feels blissful, and any thoughts you had on exiting the tub were momentarily stalled by the kiss of your beautiful mermaid girlfriend. Not that leaving would be much possible now, since your lower half was now a red mermaid tail.
But that wasn't it, your chest suddenly formed two very plump, perky breasts. They were a modest B cup, but still very round and tender. Your hair lengthens, and your overrall stature and build decreases to accommodate for the switch in sexuality. It didn't take long for the gender swap to take place, but you weren't even thinking about it as it was happening. Your mouth still preoccupied with the lucious lips of your girlfriend, as both your fishtails squirm and wrap around sensually.
"And you know what else?" your girlfriend whispering into your ear, as you look into her piercing, enchanting eyes. "I always wished for a lesbian mermaid lover...one who I would transform from person, to mermaid...with no thoughts of humanity or male gender remaining after the change." she casually said with a giggle. Her deepest, darkest secret fantasy having been revealed to you, and all you could do was giggled as well and go back to making out with your lovely girlfriend, those such thoughts of being a human male long gone.