Offline/Explain why you wanted this cabin
"Just sit down and hear me out, okay?"
It takes her a moment, but she does step away from the door, sits down on your side of the cabin, then looks you up and down with a confused mix of disgust and amazement. What a way to shatter your little sister's innocence, having her walk in on you fucking her goopy playdough. You just hope you can win her over.
"The whole point of coming out to this cabin," you start, struggling to contain the mess that is attached to your cock, "was that no one else would come out here. I can do whatever I want here and not get yelled at or grounded."
"But that's no-"
"Let me finish. There are no rules here. For once, I can just go crazy and do whatever I feel like and not worry about mom or dad or anyone. But the same goes for you too you know, if you want. While we're out here you can do whatever you want to and not get in trouble for it. Why? Because I'm not going to tell on you. We don't rat on each other, okay? What happens out here stays out here. And this?" You point down at your blue dick. "This sure as shit stays out here."
"Don't swear," she quickly chastises.
"No rules," you respond just as quickly.
"But... if you wanted to do weird things with slime why didn't you bring your own? Bluey is my favorite..."
She names her slime. Of course she does. "I dunno. I didn't plan it. I just thought it might be fun. But... yeah, it's not that fun."
"Sure it is!" she says proudly and defensively.
"Yeah... how do you get this off?" You hold out your hands, the slime stretching in a lattice from your fingers to your now half-hard dick.
"You want me to show you?" she asks, excited to share her love of slime.
"Yeah, that'd help."
"It's easy. You just gotta grab it."
Emma leans in and snatches a piece from one of your fingers. It comes off in a long string, but she dabs it back down and collects more of the goo with her delicate digits until your finger is clean, and then most of your hand.
"See?" She pulls apart the portion of slime she's reclaimed with a smile. As if you aren't sitting in front of her completely naked with the rest of her goo coating your dick. She helps clean up your other hand then glances down between your legs with uncertainty. "Umm... you can do that part."
You start peeling the slime from your cock piece by piece but you're not as deft as your sister. She makes it look easy. You leave lots of flecks and strips behind as you work up the length of your shaft then have even more trouble when you realize that this stuff has worked its way under your foreskin. You pull back your sheath and pick at the tiny pieces, complaining aloud and struggling with your folds and crevices.
"You just dab it. Like this."
Emma nonchalantly reaches out and pats the head of your cock with a small wad of slime. Then she pats the same spot again and again, firmer and firmer, seconds ticking by, staring intensely at the ridge she's touching on your cock that is now well devoid of slime. She's not technically touching you, only the slime is making contact, but she's definitely watching your dick bob up and down. Once her "demonstration" ends she turns to the side and looks down into the slime she's collected in her hands.
"You can do it," she says softly, sounding surprised and ashamed that she just did that.
"Yeah. Er, thanks," you slowly reply. She may feel ashamed but you're downright astonished that she just played with your dick so blatantly, especially since you saw her trying to avert her eyes up until that point.
Dabbing until there's nothing large enough worth dabbing, you shove the remains into Emma's hands.
"Remember, this stays here. Got it?"
She nods, looking down at the blue goo in her hands. You get up so you can put your underwear back on and finally regain some modesty. Once your pants are also in place you look over at Emma to see her calmly playing with your dick slime.
"You do know that was just... all over my dick, right?"
She glares at you out of the corner of her eye. "That's not Bluey's fault."
Remarkably she bags up Bluey and takes him (it?) with her back to camp. You also head in with her after finding your shirt, in part because she's still afraid of getting lost. Apparently dad led her back to the cabin when she couldn't find you. You're lucky he didn't come in with her. You try to explain to her how to find the cabin but it's pretty much a straight line through the trees. Either she's that dumb or she's useless on purpose.
Dinner is fine. Your cousins are even wilder on day two. Emma stays up playing with them even later tonight but when she gets cranky Mom asks you to take her back again. She trudges her way through the bush in front of you, partly in protest and the rest from exhaustion. You have to push her most of the way. As soon as you get to your cabin she strips off her pants and slips inside your sleeping bag wearing her shirt and panties.
Well that's fucking annoying. But if you let her fall asleep you can probably move her into her own bag later.