Dan really didn't want to be a mount for the rest of the afternoon, but he was in no position to object. His tits needed milking, right now. He suddenly felt a heel push into his but.
"Okay mount, if you want to have a dick or your tits milked, better turn around and get me my book." Kat commanded and tapped her brothers ass again with her heel.
"Dani find book in your room?"
"Yes, the book I threw away isn't the correct one. Now move it, so I can keep my promise to you."
Try as he might, Dan found he still couldn't move his hind legs.
"Well, what are you waiting for?" Kat shifted her weight on his balls, while her her cock moved in his vagina and Dan moaned.
"Dani has trouble moving with only front legs. And Dani's tits hurt. Please milk Dani and give Dani hind legs back." Dan said pouting.
"Oh right, I guess that makes sense. Okay, let's try this."
He felt her shift on his balls again. It felt so good.
His body started tingling. What was she doing now. "Oh no!" He heard Kat scream behind him. He briefly felt two feet on his ass, she removed them again.
Meanwhile, he felt his own body starting to change. His head slowly started to recede into his shoulders, "Help Dani Kat!" Dan yelled as he felt his head slowly melt into his shoulders. He wanted to yell again, but found he hand no mouth and slowly the light faded.
The world was dark, but Dan could still feel himself changing. He felt like his consciousness was getting sucked away, jetting around his body until finally settling. The feeling to his body came first, he felt stiff. He felt a need to be touched, to be rubbed. The feeling to his mouth came second. He was drooling, his drool was sticky and had a weird taste. A taste that let him feel oddly fulfilled.
Finally his eyesight came back. He was staring straight ahead. He could move his neck, if he even had one. At his peripheral vision he noticed two short legs. He wanted so badly for someone to touch him. When he realized what had happened. He'd turned into his own cock and he needed attention. He tried to talk, but his mouth felt weird. A first attempt was a sputter of precum. He needed to be put into something. A second attempt made a soft whimper. His mouth felt so sensitive. A third attempt. "Kat?"
----
Kat had just finished her spell when she felt a strong draw on her cock. His pussy was pulling him. "Oh no!" She tried to get away. She put her feet against her brothers ass only to have them melt into them, pants and all. She put her hands on his balls, trying to pull loose.
"Help Dani Kat!" She heard her brother yell.
Dan's ass sucked her up, all the way up to her hips. Then slowly her body was pulled upright and moved forward over her brothers back. As she reached her brothers shoulders, her changes stopped.
She immediately felt a host of new sensations. She desperately needed to be milked, her cunt felt empty and was on fire, she felt a massive throbbing erection below her desperate for attention. She looked into the mirror at the most hideous centaur she'd ever seen.
Her own normal body was at the front, but she was slanted forward from the shorter front legs, leaving her brothers ass and hot wet cunt up high and clear. Huge testicles stuck back from her hind legs like a freaky saddle. A massive leaking dick run from between her legs to her front legs, while sandwiched between two large bloated aching tits.
Had she really done this to her brother? Wait, where was his head!
"Kat?" She suddenly heard a strained voice below her.
"Dan?"
"Dani is dick!"
Kat didn't know whether to laugh or be shocked. She'd taken over his mutated form and he was her dick.