Jeff gulped and quickly turned around to block his dad's view of the screen. "Oh, it's just some programming homework. I'll get it finished then come meet you downstairs." For a moment it looked like his dad was going to question that, but then he just smiled and ruffled Jeff's hair. "Ok buddy. Would be really cool if you wanted to watch the game with me. See you in a minute, champ."
He then turned and walked off, leaving Jeff sighing with relief that he didn't have to explain the strange situation. Then it occurred to him that maybe his dad would be a good choice to test the machine on. That way, if it went wrong, Jeff could just revert it.
Scrolling through the options, he was intrigued by the anthro packages which included a few separate changes in one themed group. In particular, he was tempted to try the anthro lion package titled "Father of the Pride". The short description claimed that it was a lion anthro transformation including masculinity and strength upgrades. He didn't notice the small warning text underneath which described it as a fetish package, and to check the additional effects. He clicked it and set up the target as his dad, before pulling the duration down to just one day, since it was supposed to just be a test.
The transformation program started to run, and Jeff noticed that the time required for it to complete was a few minutes, so he might as well head downstairs and watch it take part. He stood up and walked out, making sure to lock the door so that no one would be messing with the program. Downstairs, his dad Mike was sitting on the couch, two pizza boxes open on the table in front of him. Mike was wearing cargo shorts and a red t-shirt that was tight against his firm pecs and slightly round belly, his arms thick and strong and stretching the sleeves a little. His chin was stubbly and he was hairy all over, being quite a masculine guy. He was also wearing sneakers, as he must have put them on to get the pizza from the delivery guy. He looked over as Jeff walked down and smiled. "Heya son! Wasn't sure if you'd be joining me. Take a seat, the game's only just started."
Jeff sat down, not really watching the game and instead keeping an eye on his dad as the older man watched the game. It didn't seem like anything was happening. Maybe Mike's biceps seemed to be straining a little more against his shirt, and something about his hair looked a little off. Jeff looked closer, trying not to seem suspicious. Where his dad has previously had streaks of grey in his hair, the hair seemed lighter and shinier, almost golden. It also seemed longer, sticking out at the back much more than it used to be, and his fringe slightly over his eyebrows. Mike yawned, and Jeff's eyes went wide as he say his dad's teeth stretch and grow into large, sharp fangs. When he finished yawning, he stuck out his tongue, and it grew long and wide, turning a brighter red as he licked his nose with it. When his tongue moved away, his nose had turned darker, and the shape had shifted into a more triangular, feline form. It was actually working! Mike grunted, and spoke, his voice deep and growly. "Ugh, these shoes arrrre rrreally tight." The tips of the sneakers seemed to be bulging and stretched, and Mike reached down to pull them off. He sighed with relief as he pulled his feet out, stretching them in the air. The socks were straining to contain Mike's feet, which were growing even as Jeff watched. They stretched longer and wider, claws tearing through the front before the fabric split completely, tearing open. Large, furry clawed toes were revealed, their golden hue shiny and inhuman. Mike put his feet up on the table, wiggling the toes as his soles thickened and bulged, forming large pink pawpads on each toe and on his sole. Jeff looked from his dad's feet to his face, wondering if Mike would react, but his dad was acting like everything was perfectly normal.
With his feet fully shifted into large feline paws twice as big as his former human feet, the changes began to move up Mike's legs. His leg hair shimmered and turned golden, his legs thickening with muscle as his calves swelled and hardened under a coat of soft fur. His thighs began to pack on muscle too, causing the cargo shorts to gradually lose their former bagginess until they were practically skintight against him. As he was staring, Jeff suddenly realised that his dad's pants were starting to tent, a bulge forming between his legs. Jeff turned red with embarrassment, then saw his dad's hand begin to slide down onto his belly. It grew wider, the bones creaking as it got larger and stronger, more golden lion fur spreading over it. The palms bulged and thickened into pads, and a set of thick, strong claws slid silently from his fingertips. For a moment Mike slid them in and out, then pulled them back in as he slid his hands into his pants and started to rub them up and down. Jeff almost called out in shock. His dad was jerking off under his pants! Jeff coughed, trying to remind his dad that he was sitting right there. "Um, dad....you feeling ok?" The older man turned and grinned, not seeming surprised or embarrassed at all. "Feeling grrreat, son. Why?" Jeff was surprised into silence, looking at his dad's huge fanged grin as Mike's mouth and nose started to push forward, creaking and cracking as it shifted into a muzzle. His stubble thickened, growing into a dark beard that began to spread up his cheeks to link up with his hair. His hair was also changing, growing longer and shaggier as it spread out into a massive, wild mane that reached all the way down his neck. His eyebrows darkened and thickened, and his eyes turned a deep gold as his face was coated with fur.
Mike stood up, the couch creaking under his increased weight. He was barely paying attention to the game, and as he stood, he seemed to stretch up, his whole body getting wider and taller as he grew almost a foot in height. His shirt was straining to contain him as his pecs grew larger and harder, his belly tightening into a hard, firm six pack. As his biceps bulged, he flexed, and the shirt tore at the sleeves. Grinning and feeling more virile and strong than he had in years, Jeff's dad pulled his shirt off to reveal the fur covering his chest. It grew thick between his pecs, forming a bushy forest of fur. It was also thick and hairy under his bellybutton, forming a fuzzy trail down into his shorts, where he was still slowly but consistently stroking himself. Gradually, his shorts started to slide down in the rear, pushed down by a growing bump at the base of Mike's spine, which grew longer and longer, forming into a strong tail. With a shimmer of golden fur, it soon developed the same pelt as the rest of him, and the tip erupted into a bushy mess of fur.
All the time that Mike had been stroking himself, he hadn't been looking towards Jeff, but that changed as the huge lion turned his gaze towards his son. Jeff was feeling dizzy and strange. His father's huge, warm body was emitting some sort of fragrant, animalistic musk. Scent flowed freely from his huge feet, and his armpits, but especially from inside his shorts. It was raw, and masculine, and wild, and made Jeff think of an exotic savannah. It made him feel a bit confused, which was the reason he didn't immediately freak out as his dad stared at him with a feral grin and then pushed down his shorts and kicked them off, standing proud and naked in the living room. His dad's cock had changed, the base now covered by a furry golden sheath, and his balls had grown massive, becoming a pair of pale yellow orbs the size of oranges. His cock was standing firm and tall, a massive rock-hard pillar of meat which he was eagerly and lewdly stroking.
The transformation was complete. His dad was now a massive, masculine and powerful lion anthro. But Jeff hadn't expected him to become a horny one!