Offline/Just tuck her in; you don't trust yourself
You think about joining her, but despite lowered inhibitions and impulsively swapping spit with her all of 10 minutes ago you just can't bring yourself to spoon your cute little sister fully bareback naked. Maybe it's your assurance to dad that you'd take care of her, maybe it's the fear of what you'd want to do with her, but you zip her up, kiss her goodnight, and fall asleep in your own bed feeling more emotionally conflicted than you've ever been.
---
"Justice?"
You awaken groggy with a headache. Is this what hangovers are like? It takes you a moment to pull your senses together. It's light outside but it's definitely still early. Emma is sitting next to you on the floor in a t-shirt. Only a t-shirt. For the second morning in a row she has blue slime on her crotch.
"I did it again. Can you get it off?" she asks, leaning back and wiggling her legs enticingly.
"Umm... yeah, sure," you reply, still trying to wake up.
She scooches forward and positions herself right in front of your face, one of her legs stretching over your body. Propping yourself up on one arm, you look her over. She hasn't even tried to take it off yet. The slime is pressed firmly against her crotch, a hand print still visible. A shameful look is on her face, her cheeks slightly rosy. You're still not anywhere near as good as your sister at this extraction technique and she surely knows it. This might just be a convenient excuse to get you to touch her, but you're happy to oblige.
Carefully, almost clinically, you peel and pick the slime away from her sex. You gingerly dab her slit clean then run a finger along the inside of its short length looking for remnants, flicking up over her clit a few times just to watch her twitch. But she's already very clean despite your amateur skillset in the slime game. Slick yes, but clean. You pinch and play with her lips a little for fun but end up passing the collected ball of goo back to her trying to maintain some semblance of a clean conscience.
"Okay, I think you're good."
"But you didn't..." She pauses, mulling over her words. "There's some inside still."
"Pretty sure there's not sis. It was only on the outside."
"Okay, but..." she sets her slime aside then pries her lips apart right in front of you, the inside of her pussy glistening. She even inches forward for good measure. "Can you just check? Please? Like yesterday?"
Your erection shifts in your sleeping bag and, only now noticing it, you shift as well. You've barely touched her but she looks visibly wet, way more than yesterday. She must have got pretty worked up just with the anticipation of this. You wonder how long she's been awake.
You reach out with one finger and slip it straight inside her. She gives a cute gasp and wriggles her body briefly, like she just got a shiver. You slide in much easier this time and shove your finger all the way inside in one smooth motion. You exercise your penetrating digit, twisting and rubbing around inside her. Even if she'd shoved a whole bag of that goop up in here you're not sure if you'd be able to tell given how wet she is. But your conscience begins to fight you a little given the pretense behind all this and you start to question taking advantage of your sister, even if she's trying to take advantage of you in kind.
"Do I need to keep going?" you ask, resting your hand.
Your sis bites her lip and nods slightly. So you wiggle some more, pulling out and pushing in at different angles. She squeezes you again and again, experimenting against your varied movements. Her breath catches a few times when you drag the back of your finger along the top edge of her small opening. Both of you know you shouldn't be doing this and neither of you say anything. But the shared subterfuge surrounding this is starting to get to you. Your headache doesn't help. With some hesitation you yank your wet finger out of your sister, inducing another visible shiver.
"What's wrong?" she asks, releasing her lips.
One last impure thought crosses your mind, but at least you can justify it. "Open your mouth," you order, offering Emma your shimmering finger. She leans down and obediently draws in your digit with her tongue. "What does it taste like?"
"Mmph..." she pulls away, sucking the juices off your finger. "I dunno. Kinda funny."
"Does it taste like slime?"
"No," she confirms, shaking her head.
"Then you're good." You sit up, forcing her one leg to open even wider and putting her off balance. "Right? Unless there's something else."
She pulls back, a bit unsteady, then stands up holding her hands in front of her crotch. "N-no."
"...are you sure?" you ask, letting her think about it and frankly wanting her to ask. She just nods innocently. "Okay. Then... maybe you should get dressed."
She furrows her brow at you. "How come? You said there's no rules."
"Yeah, well," you start, opening your sleeping bag. "You keep making this happen."
"I'm doing that?" She crouches down next to you, eyes fixated on the boner pointing up from your crotch. "I didn't... I... I can hold Sparkles aga-"
*Knock Knock*
"Wakey wakey!"
Fuck.