There was no answer on your girlfriend's phone so you decided to head over to head over to her apartment to see if she was there.
---
Your girlfriend didn't pick up her phone because she had just stepped into the shower. Alison let the warm water cascade down her athletic body. She looked forward to the refreshing shower after her daily post-work jog. She would rather swim laps, but she hadn't been able to afford an apartment complex that had one. Swimming brought her as close to being a mermaid as she would ever get to be. Well, almost. Hopefully one day after she could afford to move somewhere nicer she could save up for one of those realistic-looking tails she'd seen on the internet. For now, it was jogging to keep fit. Not for anyone's sake but her own - she loved the energy that came with it.
Alison ran her fingers through her long blonde hair, letting the water rinse it thoroughly. As she stood there enjoying the indoor rain, she realized her legs felt a bit weak. She hadn't gone any faster or farther than usual, but maybe she had just been going too far or too fast lately? Shutting off the water, Alison grabbed the soap and lathered her body. As she bent over to reach the bottom of her legs, she felt extra wobbly and had to brace herself against the side of the shower. Dehydration perhaps? Better hurry the shower and get some ice water. She turned the shower back on and almost immediately lost her balance, falling back against the tile and sliding down into the tub. The lose of footing was suddenly and the collision with the wall painful, but nowhere near as serious as it could have been. Alison tried to figure out what had just happened. She hadn't slipped; her legs just stopped supporting her. Now she began to get worried. She sat in the tub for a few minutes, but the numbness in her legs only increased. It was like they were falling asleep for no reason. She tried to get up, but couldn't - her legs were limp. She reached up and turned the water off then pondered what to do next and settled on getting out of the tub as her first priority. Alison pulled the shower curtain open and climbed - or rather flopped - out of the tub with a great deal of difficulty. She twisted herself back into a seated position and was shocked to find the changes taking place in her legs.
---
Pulling into a parking space outside your girlfriend's apartment you spot her car. You call her again on your phone, but again no answer. You knocked on the door several times, but still nothing. You hope she is just sleeping very soundly and nothing is wrong. You pull out your keys and use the spare she gave you to let yourself in.
"Alison, are you here?" you call out.
"I'm in the bathroom" she replies.
"Are you okay?"
"Sort of."
You suspect the change has indeed started. "Sort of?"
"Something's happened to me. My legs...they've...come see for yourself..."
You walk through the apartment, knowing yet not knowing what to expect. You open the bathroom door to find Alison sitting on the floor and indeed her legs are gone, replaced by...