“What’s wrong, little brother?” Ben joked, groping his enormous boobs through his tight T-shirt. “Jealous?”

“Stop calling me little brother! Our body swap is only temporary!” Marion complained, her body now too short to be intimidating. “Stop playing with my breasts! And put on a bra I can see your nipples!”

“Dad says it’ll be at least another week before the machine he made gets fixed. So until then...” Alan continued to check out his body in the mirror, wiggling his tight ass in his sister’s booty shorts.

“I can’t deal with this!” Marion cried, rushing into her room and closing the door.

A while later, noticing that she hadn’t come out of her bedroom, Alan decided to investigate. He burst in and saw his sister with her pants down, head tilted back in ecstasy as she jerked off her new cock!

“Eww, little bro!” Ben laughed, his sister looking absolutely mortified at getting caught, “Looks like even you can’t resist these boobies!”

“No... I w-wasn’t... I-I was just...” Marion stuttered, trying to hide her rock-hard modesty with her hands.

“It’s fine, I won’t tell mom.” Ben said, closing the door behind him and getting onto his knees. “As long as you don’t tell her about this...” Lifting his shirt he revealed his big sister’s soft pillowy E-cup boobs and rested them on his sister’s thighs. Spitting on his former dick for some lubrication he enveloped it between his hooters and began to tit-fuck his older sister with glee.

“W-we shouldn’t... I-I’m still a virgin...” Marion protested, but it wasn’t long before the two of them were moaning in taboo pleasure, both caught up in the sexual feelings of the opposite sex.

“That’s it, little brother...” Ben said, licking his lips as he gave into the primal lust of a body built to worship cock, his hands bouncing his monstrous titties up and down his former shaft. He was already thinking of how the machine could have a mysterious ‘breakage’ that would seal them in these bodies for good. “... fuck these boobies. You were a real titty monster! And I’ll be using you every day from now on...”