“So we pull straws to see who becomes the guy?” Sarah asked

“Yep, Whoever gets the marked one, becomes the guy.” Maggie responded, getting ready to pull her stick. The pulled theirs to find that Sarah got the marked stick.

“I’m fine with that, it’ll be a whole new experience.” Sarah said picking up her injector, labeled with a blue symbol on top. She injected herself and watched as the changes began.

First she had to get through the gender change. Her hair went from shoulder length to a buzz cut in a matter of seconds. Her breasts shrank into her body as her shoulders broadened.  Her arms bulked up and started getting covered in hair. Her delicate hands surged and became rough calloused hands of a man. Sarah’s waist shrunk into her body as a six pack defined itself on her stomach. Her thighs and ass shrank and became toned thighs of a man covered in hair. The final part of the change occurred when Sarah felt her ovaries being pulled out of her body. Her womb disappeared as they made their way out of her vagina. When they made it out, they swelled as the eggs turned into sperm and more were made. Sarah’s vagina sealed up as her clit started twitching. I rose out to about 3 inches long and 1 inch thick. He knew it wasn’t big now but when he got into part two, he’d be hung like a horse. Sam now stood there waiting for the second half of the serum to take over.

Sam then felt his feet curling up, turning black as night becoming hoofs. The muscles in his legs building and becoming bigger, to support his incoming wight. Sam put his hands on his ass to find it growing out, getting bigger and full of organs. As his rear end kept expanding, his penis was pulled along with it. Fur started coating his front legs up to his navel and all the way to his back half which was almost as big as a couch now. His rear legs started growing out from the mass, touching the ground and letting him readjust the weight of his new body. A new tail shot above Sam’s ass draping over the hole. The final change occurred when Sam suddenly felt his small cock get hard. A bit of fur grew over the original base, the tip flattened out and grew foreskin. It started crawling up his stomach, getting longer and thicker. His balls swelled and started to hang from his body, filling more and more with semen. He let out a small moan as his cock reach a full foot long and 5 inches in girth. He came right there onto the floor, which the covered Incase this happened.

“Wow Sam, do you want me to have some fun with you before I change?” Maggie asked.

“If you could please.” He said moving to give her a better position.

Maggie got down under his new body and tried to start jacking him off only to find that she couldn’t fit her hand around his massive cock. Maggie used both hands to simulate Sam who started giving out small moans. Maggie started spitting on the equine penis and put her lips on the flat tip. She tried to force her way down the late cock but quickly met her gag reflex. So she swirled her tongue around the meat she had. Sam was clearly enjoying this from the mix of moans and horse noises he was making.

Maggie reached forward and gave Sam’s dangling balls a nice tight squeeze. Sam let out a full blown whiney before cuming into Maggie’s mouth. There was so much that Maggie couldn’t swallow it all, letting it dribble down her body. “I think it’s my turn to change.”

Maggie grabbed her injector and didn’t waste any time. She injected it right near her vagina so it would be the first to change. Maggie started moaning as her entrance started opening wider, she reached dow to find that it was more sensitive and rubbery. Her clitoris swelled and became the size of her thumb. She touched it and screamed out in pleasure. Fur started to spread where her pubic hair was, quickly covering her navel down to her feet which were turning black and hardening.

Maggie’s leg muscles started build as her ass swelled, becoming her horse body. She put her hand on her growing body and felt the organs and muscles shifting. Her new body was becoming a little too heavy to handle when her back legs started growing out of her body. She readjusted herself as a tail grew out covering her asshole. A warm feeling grew over Maggie as her vagina relocated to her back legs so Sam could enter easier.

She knew the changes were done but the heat wasn’t gone. If anything, she was getting hotter, she felt that her womanhood was dripping wet but she couldn’t do anything about it. It then clicked for her, she was a mare in heat. “I need a stallion!” Maggie shouted, moving her tail out of the way. Sam wasted no time in trotting over and lining up with Maggie’s entrance.

“Are you ready Maggie?” Sam asked

“Yes! Just please do it!” Maggie begged. Sam reared his front legs and started humping his girlfriend. “Yes! Yes!” She screamed out, Sam’s horse cock filling her walls. Loud thuds were heard around their apartment. The sound of a loud neigh filled the air as Maggie came over and over again.  Sam knew that if he actually came there was a chance that he could get Maggie and himself stuck like this if Maggie got pregnant. The company would help them through it but they would have to give up the child.

Sam felt his balls clench and started to try and pull out before Maggie slammed back into Sam’s cock. She looked back at him, her eyes clouded in heat and lust. Sam couldn’t hold it anymore and came into Maggie. Maggie’s lower stomach bulged a bit. “Come on Sam! I know a stallion like you can go another round!” Maggie said before her heat wore off. “…oh no.”