Hot Summer Job/Tease your sis about her sleepover
"You know, it almost sounds like you girls had as much fun as I did last night."
"We had way more fun than you did! We watched movies and played games and did a buncha dares. But you?! You were just..."
"Yeah?"
"...doing gross things with their mom."
Shifting your grip as Bree continues to squirm, the droopy edge of your sister's towel grabs your attention. The thing is hardly still on her, most of her back exposed, the jump into your arms doing most of the work to loosen it. Her repeated wiggles since have only made it worse, the entirety of her chest easily spied depending on which way she's leaning. Surely her towel would fall away from her the moment you were to set her down, merely caught between your bodies, but with her legs wrapped around you she would make such a task difficult. Yet she's unconcerned at best with her towel situation, quite content to be latched onto you as you periodically switch your grip between her slender thighs and bare bottom.
"Wait, I was doing gross things? Says the girl who's been holding a giant egg in her butt since yesterday!"
"Riley!" Bree tries to look offended but it comes off as embarrassed. When she doesn't defend herself, only a shy smirk sneaking through her facade, you push a little further.
"And the girl who made her friend pee on the front lawn."
"We didn't make her..." she's quick to clarify.
"Not to mention the girl who jumped into her brother's arms without any clothes on."
Bree looks down between you, observing the perilous state of her towel with an eye of mischief.
"Well... I'm not naked."
"Well this doesn't count as clothing." You pull part of the towel out from between the two of you, pulling it away from her body and into the air as if to inspect it, then discard it, lettin it hang to one side. "And I'm not seeing anything else," you add as you return your hand to palm one of Bree's ass cheeks.
"But I'm not naked naked," she insists with a playful scowl.
"You sure about that?" Sliding a hand off of her ass, you round her butt up onto her back and find nothing but bare skin. You even pull around her side briefly and slip your hand between her stomach and her towel, driving home your point. When you slip your hand back under her you give her bum a few light pats. "I don't think it's doing much anymore."
"Okay, fine." Bree pulls against the back of your neck with one arm, digging her heels above your butt to help float her body away from yours. Little more than a shrug is needed for the rest of her towel to fall away from her, landing at your feet. With that out of the way she snuggles into you again, pressing her revealed crotch firmly into your stomach. "Now what about the boy who keeps making her sister get naked?" she notes with a sly smile.
"You mean the sister who just took off her towel?"
"No, the brother who likes to touch his sister's butt!" she retorts with a wiggle, gleefully pressing her ass into your hands.
"Yeah? And that's the sister that lets people put things inside her butt, right?"
"No, I never..."
Bree halts herself with a gasp as you guide a finger into the crack of her ass which you have been spreading unabashedly for some time. You've both been escalating this like a game of chicken, so your sister must know you're serious, but she's still thrown by your intruding finger. Not wanting to ruin things by charging ahead, you pull away to show her you're just teasing, then bring it right back to test whether she wants it.
"So? Is it the same girl?"
She glances up and down, guiltily meeting your gaze before she can answer with, "Maybe..."
That's good enough for you. Reaching further under her, you accidentally press your digits against your sister's pussy for a moment, confusing and surprising both of you. That would be another thing entirely, and not where this conversation had been going, so you pull back, sliding away to navigate your fingertip to her backdoor. Gently pressing into her flesh, you stroke round the rim once you find the pinpoint little hole of her anus.
"Yeah, I thought so. Is that maybe because she likes it?"
"Maybe you're..." You interrupt her by dipping your finger into her flexible hole. She gives a little huff, her face flush, but is determined to finish her sentence. "...h-hugging your naked sister..."
"Yeah. Maybe I am."
You both go quiet then. It's hard to know what to say when a brother has his finger up his sister's asshole. She just hugs you tightly as you slowly work your finger in and out of her bum. As you gradually build up speed, you eventually reposition her, pressing her lower back and bending slightly to get her to push her hips out. She hangs away from you slightly in this new position and lets herself drift away until she's looking up into your eyes as you steadily fingerblast her butthole. But the gaze you share isn't quite passionate or sensual; it's unnerving. You've never done this sort of thing before and it's crazy awkward to be doing it with your sister. Even as she makes little grunts and huffs of pleasure, a silly grin grows on Bree's face as she stares up at you.
"What?"
"Umm... this... is kinda weird."
You slow to a stop, your finger still inside your sibling, and smile back at her. "Yeah. Kinda. But... you do like it right?" Bree smiles even wider but she refuses to answer. Her blushing cheeks mostly answer for her, but her silence is only making it more awkward. "You, uh, wanna get dressed?"
Bree thinks about it but timidly shakes her head no. "Do I have to...?"
"Hey, mom and dad are gone all weekend, so you can do whatever you want."
"But... you're in charge, right?"
"I suppose so."
"So... what if you were to make me?"
"Make you do what?"
Bree just shrugs her shoulders, unwilling to say, then calmly wiggles her hips. Just the tip of your finger is still inserted in her bum so you can't tell whether she's trying to wiggle onto it or off of it. Regardless of her state of mind, it sounds like she's giving you a lot of power over her.