Darlene tugged at the collar. "First, let's turn me back and get this collar off."
"Oh, no no no," Sonya said eagerly. "I was thinking about this in the car. That problem at the playground gave me an idea. You were turning you into a horse, weren't you?"
"Yeah, that girl on the jungle gym wanted me to be a pony for her 'knight' brother. Pretty twisted."
"Maybe," Sonya grinned.
Darlene's eyes narrowed. "No... No, don't tell me."
"This isn't good enough for what we need," Sonya said as she gestured to the benches and the port-a-potties. "It's too public. A family could come along any minute and we'd have another mess on our hands."
"So why'd you pull over then?"
"The road tapers off after a bit. We're gonna need alternative transportation."
"Ugh. This is so wrong," Darlene grumbled.
"What are little sisters for?" Sonya joked as she rubbed Darlene's head. "First, you'll have to grow up. Back to your normal age, chop chop!"
Darlene felt her body stretching, getting taller. Her dress dug into her shoulders and waist painfully.
"Oh, lose the clothes!" Sonya said after realizing what was happening. In a flash, Darlene was fully naked apart from the collar as she completed her growth into an 18-year-old woman.
"Um...," Darlene said, looking down at her very developed body.
Sonya was red-faced. "Sorry. I had to think quick, and...heh..."
"I'm not bad," Darlene said. She cupped one of her modest breasts and trembled at the sensation.
Sonya was laughing. "You still have the pigtails! That's so cute!"
"Yeah, how about we do something about that? And why am I still a girl?"
"Because I love seeing you uncomfortable," Sonya teased. "Anyway, it's time for the rest. You're going to become a centaur. A proper steed for my exclusive use."
"Give me a break," Darlene sighed. The first changes had already begun. Her weight shifted as her torso grew longer. Two nubs emerged from her belly and gained the look of hoofed forelegs. Her existing legs twisted and bulked up into the powerful hind legs of a horse. Her balance was impossible to maintain as her torso surged upward and her forelegs fully formed. She fell forward onto them, hitting the ground with two heavy thumps.
Sonya was watching the changes with sparkling eyes. She was amazed by her boy/girlfriend's impossible transformation but also thinking carefully about what changes were to come. "How about brown and white fur? That should look splendid. And not just on your horse half, but all over your body. You're going to be a full anthro horse taur."
Darlene felt her face stretching as it did before, in the playground. She gained a horse-like muzzle, complete with long pointed ears. Her arms changed to look more like her forelegs, and her fingers merged into each other, leaving only three fingers on each hand. Brown fur covered her entire body, with small white spots in places. Large areas of white fur appeared, on her forearms and hands, at her hooves, and on the front of her neck, going down her chest and swooping underneath her horse half to her rear end. A patch of white fur resembling a diamond appeared on her forehead, with a line leading to the tip of her nose.
"And your hair can come loose and turn red, like mine. Your tail, too. You're going to have a proud mane."
Darlene's pigtails came apart in a flurry as if a strong gust of wind was tousling them. Red hair also grew out of the back of her neck and down the spine of her human torso. It became long and thick, bushy and mane-like, but soft as well. It fell around her human half in a beautiful cascade of fire red. Her tail, long enough to brush the ground, twitched behind her.
Sonya beamed. She walked up to Darlene, now a foot or so taller than her. "You look awesome," she said. She reached up and embraced the centaur, burying her cheek in white fur. Darlene returned the hug gingerly, not quite finished assimilating the changes that had just happened to her.
"Okay, one last thing and then we can be off," Sonya said. She rounded Darlene's flank. "You will don a saddle and bridle."
"What, no bareback?" Darlene scoffed, half-joking, half-disappointed. "Why don't you thfffww--!?" She was suddenly muffled by some kind of rod in her mouth. She tried to pull it out, but discovered that it was a horse's bit, firmly attached to a bridle that strapped across her head and jaw. It rested in the back of her muzzle on her gums, and there wasn't much she could do about it. A tightening sensation on her back was surely the saddle appearing.
Sonya watched as reins grew from the bridle and looped over her head to rest on her horse back. "All right, now were' in business," she said. "How are you feeling?"
"Like a priffner," Darlene said through the bit. "Juff don' make me to go for the Friple Crown."
"Don't worry, we're not going very far," Sonya said, although Darlene didn't find that very reassuring. Sonya hefted herself onto Darlene's back and placed her feet securely in the stirrups. She grabbed the reins and gave a gentle tug.
"Wha are you dooig?"
"I'm trying to guide you." Sonya continued to pull on the reins and Darlene felt the bit applying pressure to different parts of her gums. "When I tug like this, you turn left. When I tug like this, you turn right."
"How abou' I jufft go into fhe woods?" Darlene said. She reared onto her hind legs, bellowing a high-pitched neigh, and then began running down the dirt road.
"If you were trying to throw me off, it didn't work," Sonya shouted as Darlene galloped off the path and into the forest.
"Ah well," Darlene responded. "Jufft tell me when we get far enuff. Thiff fing is reely uncumfftable!"