Dan had to stop his sister before she got his friends, charging he knocked her to the ground with a squeal, his new mass making him far heavier than her. "What are you doing! You digusting pig! get off me!" Screamed Kat in protest.
As Kat tried to crawl away Dan grabbed hold of her pants with his teeth, soon tearing them off in their struggle. Suddenly freed of Dan's pulling Kat fell forward landing square on her wand, with a snap it cracked in two and a flash of energy shot from within it, hitting Kat square in the chest. She had just been hit with a full blast of the wand's remaining energy, energy that had been just used to perform a pig transformation spell.
Dan was in prime position to see what was about to happen, fallen forward, ass in the air, her pink and white striped panties showing Kat began to transform. Her ass began to rapidly swell as she gained weight, her panties pulling tight into her expanding ass crack. With an accompanying squeal Dan watched as a curly tail erupted from above his sisters ass, the final straw it tore her panties away.
Now exposed Kat's vagina slowly pulsed and expanded, pink flesh darkening as her now gaping sex became a sows. Dan felt his porcine cock grow errect, his instincts taking over, he was mounting his sister before he knew what was happening.
As Dan began to pound away Kat could only squeal in horror as she continued to transform. Her body now huge and fat was too much for her shirt and it tore along her back, falling to the floor and leaving her with only her bra clinging to her body. As Kat watched her hands morph into trotters she was finally given relief from her bra strap as it snapped and her boobs flopped free.
Her arms and legs now stumpy pig legs Kat could now better support Dan's weight as he plunged in and out of her. Unable to resist her new instincts any longer she began to match his thrusts as her huge rear wobbled and squelched as Dans sweaty balls slapped against it.
Her changes nearing completion Kat squealed once more as rows of teets formed along her stomach, her swollen breasts morphing to match. Kat's ears stretched out and began to flop back and forth with her mating. Finally her face pulled forward into a snout and she completed her transformation.
As if he had been waiting for the spell to end Dan grunted and began to unloaded thick ropes of pig semen into his sister. Both siblings saw stars as Dan's huge cock pulsed within Kat, and they collapsed to the ground exhausted. "Unhh fuck... get out of me!" Snorted Kat, now both pigs they could understand each other. "I can't, I think I'm stuck" grunted Dan in reply. "You're friends are going to see us!" squealed Kat. "Serves you right, now they'll see you as the fat sow you really are!" Replied Dan, emboldened by his mating. "Yeah, your fat sow you idiot..." Kat replied as she accepted her fate, laying forward she decided she may as well bask in the afterglow before they were interupted.