Usually, Ben would have to wait for a time when Grandpa Max was away for a long period, or otherwise wait for a time and place where the two of them could vanish for awhile without suspicion arising.
But tonight, Ben intended to get more than that.
He'd recently stumbled across something rather interesting in the RV: a bag of old Plumber items that Max had stored for safe keeping. Among the various trinkets and creature specific weapons was a bottle labeled Sleep Tonic.
A few drops on the skin would have anyone or anything unconscious and unresponsive for up to ten hours, and would wake unharmed and refreshed.
Apparently they'd used it to calm otherwise agreeable aliens that had been driven into a frenzy for whatever reason. But Ben had thought of something else to use it for.
He waited for Gwen and Grandpa Max to lay down for bed, knowing that when Max was asleep, he'd be down until a bit passed sunrise no matter what happened inside the RV. Just a few drops of the tonic into the glass of water he had before bed. When he heard Max lay down, he crawled out of bed and approached his cousin carefully.
He made as little noise as he could so as not to wake her as he removed her blanked as well as his pants. His cock grew stiff in anticipation as he carefully slid down Gwen's underwear and rolled her onto her stomach. He paused a moment to make sure she hadn't woken, then slowly moved into the bed behind her.
He resisted the urge to grope or smack her bubble butt in favor of spreading her ass cheeks gently. He quietly spit down onto her puckered hole to lubricate it-more for his own benefit than hers-before pressing his tip against it.
Ben moved his hands to Gwen's hips before thrusting forward roughly. Gwen's eyes shot open at the painful feeling of her anal walls being forced apart. She let out a confused and pained shriek as Ben grunted in pleasure, holding Gwen down as he tried to work his cock deeper into her formerly virgin ass.
"W-what the hell are you doing?!" Gwen whisper-shouted as more awareness returned and she realized what was happening. The hot pain was only spread with each careless thrust from her cousin.
"You remember our deal~" Ben chuckled, smacking her ass before returning the hand to Gwen's waist. "B-but-"
"No buts except yours~" Ben laughed at his own joke as he forced himself even deeper into Gwen's hole, shuddering in pleasure as her body clenched around his cock.
"Y-you'll wake Grandpa!" Gwen groaned, gripping the bed beneath her to try and push herself up or pull away, unable to do both as the pain grew more intense.
Ben shrugged, "I'm barely making any noise at all," He said, "You're the one who keeps shouting."
"Because you-Ah!" Gwen cried out, face flushing redder at the sound as Ben continued to drill into her ass without mercy.
Realizing that Ben actually wasn't going to stop and she couldn't make him, Gwen resulted into covering her mouth with her hands as he took his time stretching her asshole to accommodate his dick.
Ben had no idea why he'd waited so long to fuck Gwen's ass, but he didn't think he ever wanted to go a day without using it from now on. He leaned over her now territorially as his cock finally hit to the base inside of her. "Your ass feels amazing~" Ben moaned into Gwen's ear lewdly, "I think I'll use it all night~"
Gwen tensed in worry as Ben started to thrust, fucking her down into the bed as he started to cum. The hot cum flooding her bowls made her scream into the bed again, and while it at least helped better lubricate her ass, she whimpered as she realized Ben really was going to try and stay up all night to use her.
He'd made this decision before they'd even started of course, but he could feel her body tensing up nervously as he said it, which just made the moment that much better for him. And he intended to make good on his word.
And he didn't seem content with just stretching it out. Soon his smacks went from every few minutes to every few seconds, as though he intended to leave permanent marks of his hands on her ass.
Gwen pressed her face into her harder into the bed, trying to muffle herself against it as Ben turned her ass as red as her face; first with just his hands, groping and kneading and spanking her.
She couldn't tell if he was obsessed with her ass, her screams, or both, but hoped he'd tire himself out with it already. Unfortunately, the more he played with her ass, the more energy he seemed to have to keep doing so.
And when Gwen seemed to have gotten used to the smacks however, Ben switched tactics. He gave her no warning, simply bringing the wooden paddle down hard onto her already sore ass to punctuate another rough.
Gwen more gasped than shouted on the first strike, but a loud, pained cry sounded through the RV on the second, "Stop.. please.." Gwen pleased, hands moving to rub her already punished ass.
Ben rolled his eyes, striking her again, and again, and again. His thrusting into her actually slowed for the first time since he'd started as more attention went to abusing his cousin's fat ass.
He only came to a stop when cumming, quite literally getting off on how he was treating his cousin. He set the paddle aside and slid out of her ass, enjoying the sight of it leaking his cum before pressing his stiff stiff dick between Gwen's cheeks, squeezing them around his shaft and beginning to thrust between them.
Gwen's eyes had started watering from the paddle, and Ben using her ass to stroke himself wasn't exactly helping the soreness go away. The only good that came of it for sure was the spread of his cum across her stinging ass, which at least helped it cool down a bit.
But even then, his squeezing her cheeks together around his cock was only making her poor ass hurt more. And Ben had barely gotten started with Gwen's ass, and the knowledge that he could make as much noise as he wanted only excited him more upon seeing how nervous she was about it..
Gwen winced and whimpered as Ben slid his cock against her ass, hoping he would satisfy himself with this, but knowing from experience that her cousin tended to have a few rounds in him, and was rarely nice about how he got to them.
Sure enough, no sooner had he finished painting Gwen's back with his seed was already working on the next round; slamming back into her poor ass before it had even finished gaping from the first two rounds.
Gwen screamed out, unable to keep it in this time. She could only hope that Max wouldn't wake and see what they were doing.
Ben, knowing he was safe, simply continued to enjoy his night, cock pumping harder and harder into Gwen's ass. Gwen pleaded for him to stop or at least slow down so they didn't get found out, but if anything Ben took this as a challenge to see how much noise he could make his cousin make.
He pulled her arms back, using them like handles as he ground his cock harder into her formerly virgin hole. The bed shook from the haphazard pace, Ben's hips slapping into Gwen as he forced himself to the base inside.
"So tight~" He grunted as he pumped into Gwen mercilessly, savoring the feeling of his cousin's tight backdoor squeezing his throbbing, greedy cock, "So good~!"
Gwen's arms grew sore as well now as he continued to pull them back to rail her harder. His intense pace continued to shake the bed, making it squeak noisily and knock over items on other nearby surfaces from the vibration.
Lacking the knowledge that Max couldn't be woken by anything shy of an electric shock, every sound sent a pang of fear through Gwen's body that made it tense; making her even tighter around Ben's cock. This only encouraged him to fuck her harder, which made more noise, feeding into the lewd, lustful cycle.
In the position she was in, Gwen didn't have any way to cover her mouth or muffle her screams aside from gritting her teeth; a tactic that only worked so well and was getting harder to do the longer Ben used her ass like a stress toy.
And he showed no signs of stopping whatsoever. He'd let go of her arms and leaned over her body more, rutting into her ass like a dog. Gwen tried to cover her mouth again, but couldn't with how Ben's were wrapped around her.
At this point even the sounds of skin slapping against skin was getting frightfully loud for Gwen, and Ben, seeming to enjoy tormenting her mentally as well as physically, made a point of moaning out as loud as dramatically as he could when he came.
A moan she was then forced to drowned out by the hot white ropes burned inside her body, forcing out the loudest sound yet. Ben shook as Ben pulled out of her, not realizing that Ben didn't intend to stop any time soon. Ben rolled Gwen over onto her back, letting his cum soak into her bed as he sank back into her ass.
As the night went on, Gwen didn't understand how Grandpa Max hadn't been woken by all the noise. But stranger, she realized some hours in that she hadn't passed out either.
She'd never been used this roughly for this long in any context, surely her body should have given out by now; but every time she started to pass out, she felt Ben's cock in her guts and was shocked back to full awareness.
The sleep tonic wasn't all he'd found in that Plumber bag; he'd also found its antidote. If someone you didn't want asleep were to get flashed with the tonic, you could wake them instantly with its antidote instead of having to sleep it off.
Or, as Ben had realized, you could use it to keep yourself up and rearing to go all night long, each moment being as though you'd just woken up. Gwen had been dosed with it like Ben, albeit without her knowledge; a few drops in her tea to keep get up and ready for him all night.
Gwen didn't understand why she couldn't just pass out for the night, let Ben have his fun without her having to feel it. Ben didn't feel the need to explain himself to her; he was just having his fun.
He'd give her a break so she could clean up.. Sometime around sunrise.