Gym

"Da Bomb Gym" was a popular fitness center. It thrived because it was affordable, professional...

                    
                                        ...and full of eye candy.

                                           
That also included James, a trainer, and a huge reason for many female members to show up. James was popular, nice, and attractive as well as being the best trainer the gym had to offer.

However, not everyone was a fan of James. Danny, the second best trainer, was tired of losing clients and prospective hookups with gym girls to James. He was prepared to do something drastic, but he didn't want to get fired for doing so directly.

                                          
However, there was a couple that frequented the gym named Don and Christiana. Don wanted to try a different gym, but Christiana insisted that they go to Da Bomb Gym.
                              
Don assumed that it was because Christiana had a thing for James, and Christiana teased him by agreeing. This secretly made Don extremely jealous, and his buddy Danny had picked up on that. Danny then proposed a sinister plan that would benefit both of them... 

As James was showering in the men's locker room alone, Don suddenly began to sneak up behind him with a bottle in his hand. It was a bottle of "Femini" (pronounced like "gemini"), a strong magic-based female growth hormone formula that Danny had supplied him with. As Don squirted the magic liquid all over James, the startled trainer immediately turned around to fight Don off. The wild struggle for the bottle in the shower ended up slathering both men in Femini. As the two muscle bound men fought, they could already feel their bodies changing, and could hear their voices getting higher, until finally, they felt weak and dizzy, and passed out.

                                              2 Months Later
 
               Danny's plan had worked...             

                                               ...but not the way Don had expected.
After Christiana dumped her, "Donna" started dating Danny. Unfortunately, he could not keep her from getting banned from of the gym for turning James into "Jamie", but he was still her trainer, and they did plenty of "private sessions".

Jamie was upset at first, but she decided that she wouldn't let what happened stand in her way. She would never be as physically strong as she used to be, but she was still an excellent trainer. She was not going to just quit in humiliation. She was going to get her number one spot back.
                                                            

Also, with her great physique and big rear that made her gym pants very tight, Jamie was just as popular with male gym members as she was with the female members.