Adam can't believe what happened to his chest.

After almost ten minutes, the afterglow faded enough that Adam could sit up. Feeling the shifting weight on his chest, he looked down. There, perky and proud, sat two sizeable breasts crowned by stiff, pink nipples. Adam couldn't tell the size, he was a guy after all, but he would have expected to find knockers like this under the Big Boobs tag on his favorite porn sites.

Mesmerized, his hands slowly went up to his tits. Hefting them, he was surprised how heavy they are. Shaking them a bit, he watched how they jiggled. 100% natural. Technically. The movement sent shivers down his spine and made his libido rise again. What did these pills do to him?!

His nipples got even harder, big as pencil erasers. His breaths deepened along with his arousal. He couldn't resist pinching them, which elicited a soft moan from him. His own breasts were irresistible to him, and he kept fondling, kneading and pinching softly.

Behind him, the newborn slut's actions were having an undeniable effect. Despite having cum enough to completely soak the sheets, the sounds from her brother made the blood flow into Sarah's groin with ****. From where she was lying, she could even see his side-boob! Her little brother's tits were big enough to be visible on both sides of his torso! Within seconds, she had another raging boner.

She got up on her knees and moved towards him. Adam, engrossed in his ministrations, did not notice her until her throbbing hard-on slid between his legs, well lubricated from the first fucking and the precum that was once again flowing freely. The cock slid along his swollen labia, parting them slightly and making him moan deeply.

Somewhere in his lust-addled mind, he realized that this was all due to the addicting properties of Growth-X pills, but his more conscious side did not care at all. He needed the monster that was poking out from between his thighs inside him! He needed that goopy jizz shooting into him, filling him to bursting.

"Oh fuck, Sarah, I need you to fuck me! Give me--" he started saying, only to be be shoved down on his face, his hands still playing with his hooters. His cheek was sticking to the soaked sheets, but the smell of cum and pussy juice only served to make him hotter, more aroused.

"All you had to do was ask, brother dear," Sarah said, smearing his ass with her pre. She wanted to experience that tightness once again, wanted to shoot her cum deep into him. Her desire made her shaky, and her aim suffered a bit. With one frantic shove, the first half of her dick went into her brother's ass.

"Hnnngh," was all Adam got out. It felt sooo good! Almost as good as his pussy, but different somehow. Sarah on the other hand was amazed at the tightness, making her grunt an moan lewdly. Despite her meaty rod being so well lubricated, she had only managed to fit the first half in on the first stroke. Grunting with the effort and gripping his hips for leverage, she kept pushing and slowly, inch by inch, her dick went into Adam's butt, stretching him out. Adam could not do anything but gasp and moan. He even forgot to continue playing with his breasts.

Once Sarah had bottomed out in his virgin ass, she started bucking her hips, careful to always keep at least a third of her penis inside as to not slip out completely. The sensation was amazing. Adam's moans rose in volume, almost drowning out her own, after he got used to the pleasure and continued fondling his boobs. One of his hands crept down to his neglected pussy that was twitching against the air, drooling its clear juices onto the sheets. He pushed one finger on his clit, rubbing it up and down spasmodically. Not used to the sensation of having three different erogenous zones stimulated at the same time, his arousal mounted fast and after half a dozen more strokes from his sister, his orgasm raced through his body, making every muscle in his body shake.

Sarah took that as a sign to increase the strength and speed of her thrusts. Each of her jackhammer blows drove Adam forward a bit, dragging his breasts over the slippery sheets, the stimulation prolonging his orgasm. His twitching anal muscles gripped Sarah's turgid pole tightly, massaging it deliciously. She could feel her load rising in her balls and did nothing to hold it back, instead intensifying the bucking of her hips.

Within seconds, she was blasting rope in her brother's insides once more. It being her third cumshot within less than half an hour, the volume was decreased, but the feeling itself was terrific for both Adam and herself. Spent, Sarah slipped out of her brother's backside, leaving it gaping slightly. Adam on the other hand fell sideways and kept idly groping one boob and jilling his clit. Maybe he could keep the feeling of the afterglow even longer this time.

Sarah's eyes fell closed. After the intense fuckathon, she was exhausted. Soon, she was breathing softly, deep asleep. Adam, cum pooling under his butt, soon followed suit.