Cal felt weak and powerless, so he took a nearby wooden chair and slumped onto it. Then he stared at his naked and sweat covered sister who was sitting on the floor right in fron of him. Her pussy was still leaking his semen and her eyes gleamed with an inner fire he'd never seen before.
Peter and Mark were sitting on the floor, too, but they seemed to be intoxicated by the musky smell Katy radiated... or taumatized... whatever. Both boys were masturbating their hard and semen-stained cocks slowly. Their clouded eyes looked into nothingness.
Cal wiped the sweat from his forehead and tried to think straiht for a mere second, but his sisters' gaze had him locked in place, unable to think about something else but what had happened some moments ago. He felt nothing but the wooden chair beneath him and an undescribable lust for sex. As if his recent orgasm only had pushed him to a higher plateau of aroused need.
He had fucked a doggy bitch! Then this dog had changed shape and turned into his sister right before his eyes. He had felt her muscles warp and turn beneath his hands! But he couldn't stop himself. Her musk was too strong and it clouded his mind even now. He had to continue fucking her... and it felt great.
"What are you thinking about, bro?" Katy asked smiling. Did her canines look longer and sharper? One look into her eyes and he didn't care about it any longer.
"What... what just happened... was..." Cal started, his voice sluggishly and powerless, his body still slumped onto the chair.
"The way of nature, bro." Katy said murring, ending her brother's sentence for him. Then she rose to her feet slowly and with unnatural grace. Her gaze touched Mark and Peter just for a mere moment and as Katy saw them still enthralled in their own lust for traumatized masturbation, she directed her attention back to her naked and still very aroused brother.
"I've been touched by a gift that's so arousing I have to share it with you, bro." Katy told her brother while slowly moving her fingertips (her nails had grown a small tip and changed colour slightly into a darker shade) over his well formed chest.
"You've already touched it's power and now I can feel it inside of me calling out for you to join me in my new life. You have been chosen Cal. You have been marked by the beast when you accepted the necessity to mate with me in my new form."
Cal stared at her sister's beauty and even as he did not understand a single word she said. He inhaled her smell and longed for her firm breasts and her still dripping vagina. He wanted her. He needed her.
Without further delay Katy snatched the collar from the floor and snapped it around Cal's neck. It was hard for her to share the collar with someone else for even a short time as she herself felt the need to wear it. Her body cried out for the pleasures only her new bitch-form could promise. But the call to mark another human, a male, with the curse of the beast was just as strong and so she accepted her task.
Cal did not resist, too, as he was fully enthralled by her smell and her slow and erotic body movements.
"Now feel the beast awake, brother... mate..." Katy whispered.
Cal accepted the collar without interference. It smelt leathery and nice and felt to be warm to the touch. Then, suddenly, his eyes widened abruptly as images of mating dogs filled his mind in the fraction of a second and hammered away his humanity.
A low growl escaped his half-opened mouth and Katy could already see his canines grow a sharp point.
Smiling, Katy stepped forward a little and sat down on her brother's lap, guiding his already changing cock into her dripping hole. She wrapped her arms around his upper body and felt the fur grow as well as she saw it.
Slowly she rode her brother's cock while she ws sitting on his lap and started kissing his already forming muzzle.
Now Katy could feel her brother's knot expand inside of her pussy and she laid back her head in a display of unnatural ecstasy.
"You'll be a great dog, bro" Katy whispered...