Romp/Sit her on bed
You can't help but notice your sister's tits bounce up and down as she sits on the bed, and you seem to enter some sort of trance as you gaze at her body. Until recently you'd never really paid much attention to your sister Rachel but since she hit puberty (relatively late) a couple of months ago, you've taken every chance you could to check her out. The growth spurt doesn't seem to have affected her height (she's only five feet tall) but her tits have filled out to a healthy C-cup and her ass has gone from slim and boyish to just the right amount of round and curvy. As you take in her dark red pixie hair cut, green eyes, pale skin and fantastic body your cock twitches and somehow gets even harder than it was before. Only as you feel a warm breeze on your cock do you finally snap out of your daze.
"I said, do you want me to touch it?", your sister says, looking up at you with her big green eyes as you realize it was her breath on your cock that had managed to get your attention.
"Err, yeah of course," you say, trying to act cool and hide your surprise. You thought she would take a lot more convincing but in fact she seems quite eager. Maybe she has some secrets of her own?
You take a sharp intake of breath as she clasps her two small hands around your raging cock. Her fingers are cool to the touch and give you a wonderful cooling sensation as she slowly starts to move her hands and up and down your dick.
"Is this OK?", she asks quietly as she bites her lip and shyly glances up at you.
"Yeah, it feels amazing actually," you reply with a smile. Despite being the instigator of this situation (and desperate to fuck your little sister) you're struggling to comprehend how happily she has taken to stroking your cock. "Aren't you gonna freak out or something though?" you ask. "I mean, I dragged you into my room while I was naked and had a massive hard-on! Shouldn't you be running out screaming for Mom or someone..."
"Only if I wanted her to join in," she interrupts, slyly smiling at you and increasing the firmness of her grip.
"Wait, what?"
"You heard me," she continued. "I'd only go running for Mom if I wanted her to join in, but seeing as how I've been dreaming about this for years, I'm not ready to share you just yet. Mom can wait her turn. As for me," she says as she looks deep into your eyes, "I think I'm ready to find out what my big brother's dick tastes like."
Before you can say anything, she gently places her soft full lips against the tip of your cock, kissing it tenderly. She then licks up and down your shaft a few times, cradles your balls in her hand and and slowly swallows the head of your prick into her small thirteen-year-old mouth, making you gasp as she does so. With her other hand she does her best to hold on to the base of your massive dick, but her hands are so small she can only reach halfway around your girth. That being said it still feels amazing as she slowly starts to bounce her head up and down on your cock.
Still not quite believing what a great start to the day you are having, you stand there in bliss as your little sister slowly gets better and better at sucking your cock. Before long she is going at a rapid pace, with lewd sucking sounds filling the room as her saliva coats your cock and dribbles from her mouth, down your cock and onto the floor. She is almost deep throating you now, as you can feel the tip of your cock brushing against the back of her mouth. Long strands of spit hang from her chin and your dick as she pulls your cock out of her mouth to take a breath, before she grabs both of your butt cheeks and pulls herself onto your dick in one smooth motion, taking you in all the way to the base.
"Holy shit!" you exclaim as your feel her throat constricting as she gags on your dick. You expect her to pull herself off but she stays there for a few seconds, saliva pouring from her mouth and spluttering out through her nose, coating your balls and soaking your pubic hairs. Finally she comes up for air, releasing your rock hard dick from her mouth as she spits large gobs of spit onto it.
"What's next bro?" she gasps, saliva hanging from her chin and tears running down her cheeks.
You: