Offline/Em is good enough; take her back
"Oh, c'mon! We're missing the party! You're wearing your nightie. Isn't that all mom is going to care about?"
Emma looks you up and down with open mouthed indignation. But then she pauses to think about it. Her thoughts must be amusing ones as she smiles and giggles to herself before overzealously rolling both her head and her eyes at you, barking a "Fine" past her faux annoyance. When you open the door, she follows you out wearing a smarmy grin.
Your sister isn't nearly as chatty on the way back. That allows your brain to process a few thoughts in peace for a change. But there's one that grips your attention as you both pop out of the forest; Is your sister wearing anything under her nightie?
That question remains unanswered as Emma scampers off to reunite with your cousins. You try to rejoin the adults with the same party mindset you had earlier - and plan out how you're going to steal some beer for yourself - but you find yourself distracted, trying to keep tabs on your gallivanting sister. You're not trying to creep on her, but you're also inexplicably keeping your distance.
She plays night tag with some cousins for a while, running through camp with a mishmash of flashlights. Then Emma and Asha wander off together, presumably to Asha's cabin, until you later spot your sis sitting slumped in a camping chair by herself sipping on soda, idly kicking her legs toward the fire. Her nightie is at the tops of her thighs, and you do try to peek past it more than once, even going so far as to kick at her feet as you walk by, but your investigation remains unresolved.
When some of your girl cousins start to dance your spirits are uplifted, hoping that Em's nightie might be as well. The girlfriend of your cool older cousin Jet gets things started, dancing with another girl off to one side, out of the direct illumination of the fire but relatively easy to see. Your cousin Nicole joins them, and then Asha and Emma head over as well. Despite some of the older girls performing some dance moves that aren't befitting of a family vacation, most of your attention remains on your sister.
You watch Em's nightwear bounce for at least 20 minutes. It ripples and flaps and twists in the gradually cooling air as she hops energetically. The impossibly heavy hemline just can't move high enough. It rises to the edge of her bum more than once, that much you're certain, but between poor lighting and unfavorable angles you can't be sure whether you spot anything that you could consider proof.
A hand on your shoulder startles you. "You know you can go join them."
"Uh, no thanks Uncle Mike. I don't really like dancing."
"Coulda fooled me," he chuckles, patting your shoulder and walking away.
You try to keep your eyes down after that. At the very least, Uncle Dave's guitar is a lot more enjoyable when you aren't so distracted. But you find everything gets better when your focus isn't so narrow, getting back to why you had enjoyed this party to begin with.
You get to overhear some really raunchy jokes, watch a drunk Auntie Grace partake of your dad's lap after mistaking him for Uncle Mike, and spy Jet making out kinda obscenely with his girlfriend right in front of everyone. You're just starting to enjoy the inappropriateness of the drunken festivities when Emma ruins it all by asking you to bring her to bed. She wants to go to bed now. Challenging mom only earns you your bedtime as well, tied to your sister's fate.
Old enough for the responsibility to look after your sister, but young enough not to have any say in it. Just great.
"It's so not fair," you gripe aloud as you enter the cabin. "No one else has to babysit anyone."
Em doesn't take your ranting personally. She knows she's keeping you from the party. Of course she's not exactly broken up about it. "Yeah. It's really late though. Aren't you tired?"
"Yeah, of course I am. I mean... no! I'm not!" you insist, fighting a yawn. "Er, that's not the point."
"Well I'm tired," yawns Emma, crawling into her sleeping bag. You can't help but be bitter. Your sister is messing up this whole vacation for you. You had it in your head that this was going to be such a cool trip, to fraternize when you wanted and hole yourself up whenever it suited you, to be your own man in your own cabin out in the woods. Instead everything you do seems to revolve around your dumb sibling.
Staring her down with a scowl that she can't see past your flashlight, Em asks, "Aren't you gonna change?"
With an angry sigh, you toss your flashlight down then strip down to your undies. You're fuming as you get into your sleeping bag, and you nearly do resign yourself to giving in and going to sleep, but at the last moment you sit up and grab your sketchbook. Just to spite Emma, you quickly start scribbling with your flashlight tucked in your armpit, and after a couple minutes you have the outline of a clotheless young girl facing away from you with your sister's pale skinny ass prominently featured on her backside.
"Justiiiice..." she whines. You quickly close your book.
"What?"
"I can't sleep with the light on."
"Ughh... fine."
Killing the light forces you into your bunk. Not much else to do in the dark. You feel a little better now that you've spitefully immortalized Em's derriere without her knowledge, but she's still managed to ruin your night. Emma gets her way again, of course. That irks you to no end as you lay there staring at the black ceiling. You never get to do what you want.
After a few minutes replaying that thought in your head, you just won't have it. You kick and writhe in your sleeping bag in a fierce frenetic flurry which ends in you tossing your undies out into the open. It's a very minor win, but it's important. You'll sleep however you damn well please, dammit.
Petty victory or not, it doesn't help you get to sleep. It's not clear how long you've been laying there frustrated when you hear your sister begin to rustle. You're instantly annoyed when you hear her fidgeting, roll your eyes when you hear her get up, but are even more annoyed when she comes over to you. The moon seems dimmer tonight but there is still enough light to make her out when she crawls beside you.
"Can I sleep with you again?"
"What?! C'mon..."
"I'm just scared."
"The heck, sis? There's no ghosts. Go away."
"I'm still scared. I can't fall asleep by myself."
"Nuh-uh. This is my bag. You have your own. Besides, I'm naked now. So there."
"But... I'm serious. I'm really scared."
"No way. I'm sleeping in my bunk the way I want to. Period. So you and your stupid nightie can get back into your bunk, thank you very much. We are playing by my rules now. I'm not gonna budge either. My way or the highway. Put up or shut up."
It feels good to air your grievances, to stand up for yourself. Emma has to think for a moment, glancing back at her side of the room. You're positive you're going to win an argument for once... until she huffs "Fine" with a heavy sigh. She stands but doesn't leave. Instead she peels off her nightie, throwing it toward her bunk.
"Wh-what? Why... What are y-"
"Now can I sleep with you?" she asks after squatting right in front of your face. You can't see much in the darkness, but you can tell she isn't wearing a single fucking thing. Neither are you, and she knows that, so you cannot comprehend why the hell she wants to get into your sleeping bag like this. It also occurs to you that she was full commando at the party, running around the fire, dancing, and more, which is a thought that comes to you at the wrong time.
Your brain is suddenly a fuzzy mess of noise, all of your objections and frustrations totally incomprehensible to you. Why wouldn't you let a naked girl sleep with you? All you can do is shrug.
"Uhhh.... suuure?"
You've gone completely dumb, unable to process what's happening. You don't even open your bag for her. So Em takes it upon herself to unzip you and crawl inside. Instantly cramped like before, she manages to zip most of the way up again before cozying up to your side. With little free space available, every inch of your shrimpy sibling's figure seems to be touching you in some way. And she's not shy about it either, pressing against your completely bare side with her kid-like naked body. If anything she's even less shy than yesterday, wiggling her head on your chest like you are her pillow and sliding one leg over yours, hooking her foot between your shins to help lock herself against you.
As she takes her time getting comfortable, Em swings her arm down off your stomach to scratch at something, and in doing so collides with your flipped up erection, you having gone stiff as soon as she peeled off her nightie. Her small forearm slips under your hard-on and her wrist bumps into the base of your cock. She pauses there, like she's not sure what she's hit, but she slides her hand out a moment later. Her palm smoothly glides across your pelvis but you can feel the back of every one of her dainty fingers grazing your excited shaft as they go by.
She smartly takes a different route when she places her hand back atop your chest a few seconds later.
This is awkward as fuck, and yet you aren't doing anything to stop it. All you can manage is to mechanically wrap your arm around her like last night, trying to pretend everything is normal. Unfortunately either your reach is longer or she's positioned higher up tonight because your hand lands squarely atop one of her butt cheeks. It takes you a moment to clue into this and you freeze stiff when you realize that you're groping the thing that you carefully sketched out however many minutes ago.
"You're touching my butt," she whispers with a giggle, entirely amused by this.
"That... it's just... where I'm comfortable, so... go to sleep already."
For once she actually listens. No snarky remarks or follow up questions or thought vomit is directed at you. You feel her eyelash tickle your chest as she blinks a few times and then shuts her eyes. Maybe she knows to only push her luck so far after getting her way yet again. Either way, your hand continues to lightly grip your little sister's pert bum, even daring to feel up the skinny cheek - just a little - when her exhales become steady.
What the hell is up with her? Did she just use her body to get her way? Does she know how much you've been staring at her? No way. It has to be more innocent than that. Was it the 'my rules' thing? Is she just following your new bunk etiquette? She doesn't have much shame, so that's the most likely explanation. All you know for sure is that your weird little sister has pressed her smooth pussy mound into your bare hip and your dick is now hard as a fucking rock.