You grab a large bag that has a label saying "Mermaid" on it. Inside you see the blue scales of the tail and a beautifully decorated bikini top. As well as a couple of accessories. You quickly lie them on the ground in front of you before you undress. As you take off your shirt and trousers, a man comes storming through and knocks you over. "Sorry mate!" he yells, as he grabs a costume bag himself and runs into a changing room and locks the door behind him. You see more people running your way and you quickly grab your stuff and head into a changing room yourself too.
You sit down on the bench and slip into the tail. Then you start wrapping the bikini top around your chest. It is uncomfortable to wear as your chest is too wide for it to fit but that won't be for very long you say to yourself. You quickly put the accessories on and finally calm down. You managed to get the entire costume on before the change happened. Now you sit and you wait. As the minutes tick by, you grow more and more aware of how ridiculous you look as a grown man wearing a mermaid costume that is way too small for you. You wonder in silence what is happening in the store outside your changing room.
Just as your curiosity runs out and you lean forward to open the door, the tail suddenly doesn't feel as if it is constricting your manly legs anymore. In fact, you can't feel your legs at all. Instead you find that you have a beautiful mermaids tail now. Your bikini top is still really uncomforable but for a different reason. You look down and see two large breasts that don't sit inside the bikini the right way causing you a lot of pain. You adjust them quickly and thighten the bikinistrap behind your back, where you notice your hair has grown much longer as well.
After checking yourself out in the mirror and being confused, but strangely pleased, with how sexy you have become, you open the door to your changing room and crawl out of it. There you see the man that knocked you over before, he has changed too.