Johnny held up the huge jockstrap after having searched through the chest of drawers. "Wow" he mouthed, grinning at the enormous pouch it possessed for what must be a truly massive manhood. Cupping the pouch, he shook his head, wondering if a) he would really grow to fill it if he put it on, and b) did he truly want to be THAT big?
His own narcissism finally got the better of him though as he glanced another time in the dusty room's old mirror, imagining his already impressive, flaccid dick dangling at monstrous proportions.
Slipping the "jockstrap" on, he was surprised just how much room even his cock had in its generous cup. The space there was absolutely huge, and Johnny was about to find out why...
What Johnny had mistaken for an over sized jockstrap wasn't a jockstrap at all, but a chastity harness for a stallion. The ample pouch was so large not because it had ever been designed to fit a human dick, but a well endowed animal's.
At first, nothing happened to Johnny, he paced the room, and kept checking the mirror. Finally; however, the previously felt tingling sensation returned to his body, stronger than ever this time.
The pouch began to fill, and fill rapidly. Johnny couldn't help but groan as he felt his cockhead shove against the jock's material and his entire manhood thicken and expand. "Oh, Jesus..." he said, as his balls began to swell as well and weigh heavily down in the jockstrap, his testicles' outline now clearly visible, each sphere the size of a softball.
Johnny couldn't help it as his hips gyrated and he started rutting his concealed, growing cock against the air. His entire body felt like it was now on fire, and the pleasure being provided from its rapidly expanding manhood into freakish proportions, was barely covering up the unmistakable pain the rest of his form was being inflicted with.
Eyes tightly shut, Johnny felt itchy all over as his skin became thick, ebony hide, his once tanned flesh darking to black in color, and fur sprouted from beneath it. His muscles grew, his body taking on a lithe, athletic shape: his taut skin showing ever striation underneath.
Johnny groaned as he felt his feet give out under him, causing him to fall onto the ground.
Hands breaking his fall, Johnny could feel his entire body expanding, and he let out a sharp scream, that almost sounded like a whinny. His legs' bones reformed, becoming more equine in shape and proportion. Hamstring muscles thickened, and his spinal column's tail-bone seared white-hot in his mind, creating a momentarily swelling of pain at his back before he felt a long extension of himself -- that he could move no less!! -- swishing hairy behind and above his butt...a tail!?!
Johnny forced open his eyes, he could feel his crotch stuffed to the breaking point, as if his cock had overgrown the ample-sized pouch and was begging to get free. The cockhead felt warm, his entire, monstrous length felt warm, like it was hidden in some fleshy part of himself, and as he looked toward the mirror, his jaw dropped, his throat unable to give out a scream.
In the mirror, knelt on the floor, looked back at him some horrible monster: half-man, half-horse. Its rear legs were entirely that of a horse, and brown fur covered its entire body. Its muscles were huge, impressive for any athlete, and its hands were thick and wide, with only three fingers and a thumb.
Johnny's ears were pointed, his face slightly stretched, a beautiful, spiked mane of hair ran down from his furry head to his...his, tail!
Trying to stand up, Johnny felt, however, the final phase of his transformation into a chastity-belt-wearing anthropomorphic horse. He whinnied loudly, the sound echoing throughout the area as his face blazed hotly, his bones stretching as his entire muzzle pushed painfully forward, his teeth flattening in his mouth as his skull became very much like a horse's.
Caked in sweat, Johnny remained on the floor, breathing heavily as the last sickening sounds of bones shifting and muscle growing reached his long, twitching, horse ears. Every part of him was sensitive, from the grotesquely, enormous dick straining in his chastity-belt's pouch, to his sensual, over sized balls, to the tight skin across his muscular body, to his swishing tail and hard, hooves.