The massive ship moved through the sea looking nothing like what it really was. Inside what looked to be a normal looking oil super tanker was thousands of people all in the process of becoming merpeople. You and your girlfriend are two of them, being transformed into a merperson against your will as part of the plan of a trillionaire to save humanity by changing some of them.
You couldn’t voice your objections or even fight back, since you like almost everyone else was knocked out floating in tubes which would carry out your transformation. The nanites in the water was programed with the design of the merperson you had made…well sort of. Your girlfriend had designed your merbody while you had designed hers. The machines nanites which are the size of cells went to work, first slipping through your skin and into your body to begin their work on your lungs.
The lungs was the first target of every nanites and within hours the work was done, slits opened up on your neck as you gained gills. Now if you did awake up and rip off your mask you would still breath. With that done everyone began to change into the merperson they had designed.
Such a massive change couldn’t happen within minutes or even hours, however it was a long trip to the meet up point and during that time the drugs kept you knocked out almost the entire time.
Every so often you did open your eyes for a moment or two or you woke up enough to feel that something was off. It was waking up for a moment or two in the middle of the night, just enough time to roll over before going back to sleep again.
You slept as the nanites went to work, the micro machines worked on increasing your muscle mass. You where never fat but you where never built like a body builder either. They worked to the point where your girlfriend had designed them on the simulator, stopping at the point that a you had a six pack but it wasn’t over the top. Your arms got stronger as well, your jaw became more defined as well. Your hairy chest smoothed out as well to make swimming easier. Your dark brown hair began to shift as well becoming a jet black and lengthened a bit. You always kept it short but your girlfriend always said she liked it longer but you didn’t like maintaining it.
Once your upper body was done, a ROV descended from the ceiling of the tube and went to work. It tied back your now longer hair into a man bun like how your girlfriend had designed it. With it rather simple process done it went back. Next door, a matching robot was busier braiding your girlfriend’s new longer silver hair and dressing her was still working.
Your legs lengthened as well and began to merge as you started to form a tail. Your feet meet at the ankles before merging, flesh growing over everything forming a tail. Your manhood which had also grown went inside your tail ready to come out when needed.
If you had been awake, you would expect that at this moment scales to start to form on your tail however instead the flesh began to change color and texture. The skin turned jet black with some gun metal grey on the front with a few large green spots. Growing out of your hips two small fins began to grow while another pair grew out of the front and back of your knees. Your feet moved vertically and became fins. Out of your lower back the largest fin grew surrounded by similar flesh which covered your new tail. It was clear now you were becoming a shark merman…a Leopard shark merman with black/gun metal flesh with green spots.
The entire process took over a week. When the process was done, the mask fell away, and you took a breath of the water which passed into your body over your gills allowing you to breath. In time the knockout drug would leave your system and you like your girlfriend will wake up.