As she surveyed the beach, Lina noticed the girls out swimming in the seas, splashing and playing and generally having fun one way or another. It reminded her of some stories that she'd read. She stared longingly at the waves and new with finality what she needed to do to finalize this world. She clutched the medallion and grabbed it.
"I wish this world was an ocean world of warm shallow seas and that everyone on this world were mermaids. Only I will know of this change."
The Medallion glowed. A moment latter she saw the sea swell up and rush toward the shore. It crested and frothed as what looked like one monster came rolling over. Oddly enough nobody but her seemed to notice. Naked girls continued to frolick, play, kiss and sunbath unconcerned. It was surreal, like an album cover she once saw online. It was a bit scary, but she knew there was nothing she could do. All this happened in a few seconds as the beach was rapidly engulfed. Just before she was overtaken she put her hands to her face. This seen was repeated around the world. Within half an hour the earth would appear entirely blue without a scrap of land above the surface of an all encompassing world ocean.
Lina was tossed off the surface, but as she removed her hands she found herself drifting serenely through warm water along with the rest of the beach-goers unharmed. She then noticed that her hands were now webbed. . Instinctively she'd been holding her breath, but as she looked about she noticed that the other girls were unconcerned with being submerged and she could he them talking. With a bit of hesitation she opened her mouth and let water flow down through her new gills.
She took a notice of two eleven year olds at her sides which were having a casual conversation. One was a pale redhead with long hair, the other was Asian with her hair in a pony tail. Like her, they now had gill slits and webbed hands, but further changes were underway. Their skin soon changed. The Redhead became vivid blue with golden lines running down her sides as well as on her webbing and face in shimmering scales (save for her lips and "eye shadow" which were a darker shade of blue). The Asian Girl turned a steely grey with dark patches on her hands. Their noses flattened out into simple mounds with nostrils on their face. Lina touched her face and something similar happen. Then she watched as her legs began to fuse together, melding into a single long form as their feet distorted into tail flukes and pelvic fins grew out. They also grew dorsal fins and their ears elongated into fins of their own. In the case of the Redhead, they were webbed with long rays, on the Asian girl they were shark like. Soon enough changes finished and any trace of leg bones in their tails were gone.
As this happened the changes continued for her as well. She became mostly a light purple with a white underbelly and blue spots and patches. Her hands and fingers had yellow spots.
At this point they noticed her and swam over.
"Hi!" said the Asian Sharkgirl. "I'm Lucy Mako and that's Tanya Sunfin." Tanya waved. "You must be new here!"
"Well...um...hi..." Lina go out. She had always loved Mermaids and even if she'd just made everyone in the world into Mermaids. "...i'm Lina."
"Well we have a nice little apartment in the nearby reef. It's at 343 Starfish Street, level twelve room eight. We'd love to have you over if you'd like to come" Tanya replied.
"That...that would be nice."
"Wonderful! Glad to make some new friends." Lucy said, clapping her hands. "Anyway, we got a cleaner fish appointment. See ya latter!"
"Bye!" Tanya said as they swam off to a collection of coral buildings somewhat obscured by the depths.
Lina swam around and took in the surroundings. There were thousands of beautiful mermaids swimming about, lounging about on the bottom and otherwise having a good time.
This was paradise.