His sister, obviously. But what is happening to her?

The first thing James heard were the pained gasps of his step-sister. She was still suffering! Slapping the door with his flat hand, he called out to her.

"Lily? Please, open up! Maybe I can help!"

"No--ooh! Get lost! I'm alrrrgh!"

"You don't sound alright! C'mon, please let me in!"

"It's just some crrr-cramps, nothing I cuh-can't deal with!"

"But--"

"Oh FUCK, nhaahaha, yeah!"

Suddenly, as if a dam had broken, Lily's moans shifted from pained to aroused, almost as loud as when she had been bouncing on James' udder. Part of him was glad their parents were celebrating 25 years of marriage by repeating their honeymoon voyage and would not be back for two more weeks, but a far bigger part could only feel his face and ears becoming exceedingly hot, his thighs rubbing together involuntarily. His lips parted slightly, lewd sighs escaping from them as he kept pressing his body and palms against the door as if he hoped to fall through the wood into Lily's room... where she would suck his teats... or lick his folds... or...

While James kept thinking how his sister could fuck him, wiggling his hips left and right so his slick labia slid against each other, Lily's moans had not abated - to the contrary, they had increased in both volume and intensity. James could hear her bed springs creak rhythmically in time with her moans - she was definitely masturbating, wasn't she? He could feel his face grow even hotter, liquid lust trickling down his thighs. James' jaw hung slack, a bit of drool trickling down his lips as his left slowly strayed downwards over the front of his body, sliding over his deflated udder and towards his slick honeypot, feeling heat wash from the swollen lips in waves. His throbbing nipples pressed into the wood, rubbing over it with his every move.

"Aaaghmmmh, it's so sensitive," James heard his sister moan, and images of her knuckles deep in her squirting cunt rose before his mind's eye, James' left clumsily trying his best to imitate the imaginary Lily, teasing over his dripping labia. His sighs turned into gasps as he imagined his sister fingering him, middle and ring finger sliding into his slick tunnel while his palm pressed into his engorged clit. James' tongue lolled out of his mouth, hot, panting breaths washing over his lips while his left worked his gushing cunt, fingers sliding in and out, palm rubbing over his clit. His legs were shaking, threatening to give out from under him, his ass and thighs jiggling excitedly, but James was much to aroused to care - in fact, he barely even noticed.

"Oh fuck, it's--agh! Getting huge," Lily squealed as James could hear the bed springs groan in protest, "It's so thick!"

While James didn't even think of stopping jamming his fingers into his tight cunt, confusion quirked his eyebrows. What did she-- she couldn't actually...? Unbidden, his mental image of what was going on inside his step-sister's room changed - instead of stirring up her pussy, Lily now grabbed a girthy, veiny monster of a cock, vigorously pumping it up and down, pre glistening on the tip. A strained groan rose from James' throat as he imagined the fat head slide into his twitching cunt, spreading it so wide it almost hurt, his juices squelching out around his fingers. A distant part of his mind screamed that this wasn't normal, that he shouldn't lust for a thick, throbbing, juicy cock, especially not for his own step-sister's, but James was far too aroused to actually care. All he wanted was for someone, something, to fill the aching void in his nethers.

The squeaking noises from beyond the door were now growing frantic, accompanied by the sounds of something liquid splattering onto hardwood floors and strained grunting from his sister. James imagined her hand flying up and down her magnificent dick in a blur, teeth gritted against the pleasure and the strain of jacking off so rapidly. His cheek was pressing into the wooden door, a thin stream of drool running down it where his tongue hung limply against it. His eyes were rolling up, completely unfocused from arousal. The squirting sounds from his pussy grew wetter as James soaked his thighs just thinking about how Lily's imaginary cock would split him open, spreading the two fingers inside his quivering tunnel apart to at least feel a faint approximation of the sensation he craved so very much.

"Oh god, oh fuck, oh FUCK!" Lily suddenly yelled, unabashedly announcing her climax, and James could hear a mighty splurting noise, followed by the sound of thick, viscous liquid splattering down. The sounds repeated once... twice... three times, Lily screaming and squealing in bliss all the while. The thought of his sister writhing and trembling in orgasm combined with the noises she made caused James' knees to buckle and slam into the door noisily, but it didn't matter to him - the motion made him slide down the door a bit, and James' enormous nipples dragging over the wood grain sent jolts of pleasure through his body, squirting a bit of milk in the process. His jiggling ass stuck out behind him, fingers still jilling his pussy.

As his lust kept mounting, James **** two more of his fingers into his cunt, which accommodated them surprisingly well, sucking them in greedily, squelching noises resonating through the hallway when James pulled his digits out again. He was oh so very close, and the guy turned cow girl knew the climax would be strong enough to reduce him to a whimpering mess, but before he finally reached the peak that was just out of his reach, Lily suddenly unlocked the door and opened it inwards.

Unprepared for his main source of support to suddenly fall away, James fell forwards, barely able to catch himself on his free arm, his giant, sensitive tits and his knees smacking into the floor painfully, but at least he didn't hit his head. This meant that his bloated up ass rose in the air behind him, fingers still jammed into his squelching cooch, but the pain was forgotten when the smell of his step-sister's room hit his nostrils: He knew it very well from his many nights of self-pleasure, but never had it been this strong - the scent of cum pervaded the air, making James drool uncontrollably, labia twitching around his fingers. But before he could look for the source of the smell, James noticed Lily standing over him. He moved his head to look up at her, but he couldn't get any further than her crotch.

His fantasy of Lily growing a cock had been right on the money - and yet so far off: While his step-sister now sported male equipment, it wasn't the velvety rod capped with a mushroom-like head and a fuzzy scrotum James had been imagining. Instead, Lily's balls were dark brown, almost black, and at least the size of grape fruits. Slightly further up, a stark contrast to her lightly tanned skin, a thick, short tube of the same color as her nuts gave way to an enormous rob that bobbed with her heart-beat, as thick as his fist, if not wider, held in both hands by his step-sister. Where her sheath ended, it was littered with darker splotches that grew more sparse with every inch. And as his gaze wandered further along the incredible length, James realized that there were... so. Many. Inches. Moving his eyes further up the impossible, magnificent organ, he marveled at the bumpy medial ring that adorned it at the 10 inch mark - that wasn't even the half way along.

From his current position on the floor, James had to strain his neck to finally see the tip. The blunted, flared, ribbed tip, still drooling small globs of cum.