Take matters into your own hands

Since Gwen was clearly incapable of dealing with her situation, it's up to you to fix it. The only remaining question is, how should you do that? Because of the magic spell, it would be easy enough to give her a handjob and she'd blow her load with ease - but where's the fun in that? No, you needed to get her hooked on having a dick, otherwise there will be hell to pay when she finds out you're knocked up.

"Let's see..." you mumble to yourself as you begin stripping in front of your sibling, who wastes no time showing you her discomfort with that.

"H-hey! The hell are you doing?" She quickly turns to look away, but you continue until you're just as nude as she is. After your earlier adventure, your cunt managed to calm down and was no longer the puffy, swollen mess of arousal it used to be. Instead, it was just a cute little slit! There's no way for Gwen to even suspect that you had a batch of semen swimming in your belly and a tampon to keep yourself sealed shut.

"Just lean back and enjoy the view," you remind her. "A huge part of the fun when you've got a cock, is the chance to see a nice pussy. Seriously. Guys would kill for that kind of privilege. You should count yourself lucky that you had your own vag to admire until yesterday." She reluctantly shifts her gaze back to your crotch, and you could see her dick bouncing in satisfaction at the sight. Her male hormones were taking over, perfect! Now you just need to make sure that those hormones keep on coming. So after some brief consideration, you approach your sister who still sat on the toilet with a stunned expression, and kneel down in front of her. "You really are useless, you know." Teasing her about her problem came natural... you embrace the base of her dick with your slender fingers, and begin stroking it gently. A timid gasp left her pouting lips. You were getting somewhere!

You softly tighten your grasp on her girl-cock, and lean forward to give the bloated cockhead a wet kiss. As soon as you do, it begins bouncing a few more times - cute! "W-what are you doing? Didn't we agree on not doing anything sexual?" She was struggling, but her defenses were breaking down by the minute, just gotta keep on going!

With slightly parted lips, you blow a cold breeze towards the crown of her appendage and coax a needy moan out of her. You're more than happy to oblige, and lean forward to take her into your mouth with one greedy gulp. It was a little weird at first, but you close your lips around her rod and simply bob your head up and down while trying to remember what the chicks in porn usually do at this point!

"That... that's kind of nice," she purrs her approval, and you smile gleefully. Whatever you are doing, it's working. To give her some more action, you decide swirling your tongue around the swollen tip while keeping the steady up-and-down motion going. It was an awful blowjob, but as the first she ever received, it probably felt amazing regardless.

Still, it was a rare opportunity to get her interested in keeping her extra bits, and oral was just one piece of the puzzle. When you allow her to pop out of your mouth, she sighs her disapproval but makes no big effort to stop you - until you take a few steps backwards and bend over the bathroom sink to display both your cunt as well as your bum to her. "But, if you want to take these for a test drive, you will actually have to put some effort into it," you point out to her while swaying your hips seductively. There's no point in doing all the work yourself. If you truly want to get her hooked, then she needs to participate - actively!

She was so pumped full of testosterone by now, that she immediately got up and approached you. It went completely as expected when she grabbed your waist and aligned her shaft with your backdoor entrance - part of her probably still didn't want to risk having a child. It hurt at first, and she couldn't quite manage to push inside. But as soon as you relaxed, she slipped right on in and buried her cock inside your rear-end! You gasped, but were thankful that she wasn't well endowed by any means. Just like a horny teenager, she immediately began humping into you, rapidly using small thrusts to bury herself inside your body, and you could only imagine the wild thoughts running through her head. She just lost her virginity - to her own sibling! Your older sister was really getting into it, and all you had to do was allowing her free access to your body. Easy!

It only takes a few more thrusts before she buries herself inside your bum and moans out loud - her feminine voice clashing strongly with the feeling of her pulsing, throbbing erection that began spitting multiple wads of cum into your rear. It's only now that you remember the unusual amount cum, and you rapidly begin feeling the effects! More and more poured forth and into your bowels, which was only made worse by the fact that your womb was still stuffed full as well! "G-...Gwen! Slow down!" Your words fall on deaf ears as she begins grinding her crotch against your perky bum, emptying her balls into you! It simply kept on coming, until you could feel the liquid mass squishing around within you.

When she's finally done, you glance down to see your belly even more swollen than before. Full of cum. It was... hard to believe, to say the least. Some of it spilled out when she withdrew, and you could hear it splattering onto the ceramic tiles below. Shutting your legs thankfully kept at least a majority of it safely tugged away.

"Wow... thanks... that was amazing!" she blurted out energetically, while you still hold onto the sink to try and keep yourself steady. "Hey, uhmm... I wouldn't mind repeating that again sometime soon," she added shyly, and you could clearly see a strong blush on her cheeks.

Success!