I'd always wondered why our parents would lock my sister's door at night, I'd asked once or twice in the past but was told to mind my business by her and parents would get cagey and avoid the subject. Emma was four years older than me, we got on okay, had the occasional fight as siblings do but I stayed out of her way as much as I could. When I started to notice girls 'that way' I of course was fascinated by her and when I hit 18 I did my best to spy on her in the shower or jerk off to the sound of her masturbating in the next room. I didn't care that she was my sister, she was hot! She'd usually always catch me trying to perv her though, I'd get a punch in the arm or chest, called a pervert and she'd not talk to me for a few days.
One summer, everything changed.
"I don't care Emma, you know damn fine the medication doesn't work. She can come round for a few hours and your Dad will drive her home afterwards," said Mom, I'd came home to a fight.
"I feel like I'm a fucking prisoner, it's not fair," replied Emma, almost in tears.
"Honey, you know we love you and you know why it has to be this way, I'm sorry. I'll talk to her Mom and explain okay?"
"Fine, sure, 23 years old and I can't have a friend stay the night for my birthday."
Emma stormed off and I got myself a drink from the kitchen, trying not to be noticed.
"You were a lot of help," said Mom.
"What do you want me to say, she's already feeling bad, me repeating the same shit you already said isn't going to help. Marcus, son, stop skulking around eavesdropping, go for a swim or something," replied Dad, I went to my room.
A few hours later Emma came to my room, she knocked and waited, learned about just walking in after she walked in on me jerking off a few weeks prior.
"Hi Em, you okay?" I asked.
"Why wouldn't I be. I need to borrow your dvd player, Lisa is coming over for a while and I managed to break mine."
"Uh, sure, you can keep it, I mostly watch my stuff on my laptop now anyways."
"Your porn you mean."
"Oh I stream that, why would I have disks?"
"Whatever perv, can I have it or you just going to talk all day?"
I unplugged and handed her my dvd player, got a 'thanks' and she left. I sat reading by the pool while Emma's friend was round, she was a bit of a bitch and Emma wouldn't stop her if she was rude to me. I sat with my parents watching tv on the couch when it got dark and must have dozed off, Dad left to take Emma's friend home and Mom dozed off too, she always woke up grumpy so I pretended to be still asleep when she woke and went to bed. She put a blanket over me before she left though. With the room being dark, Dad didn't notice me when he got home, he put his keys on the counter and just went to bed.
I dozed off again but woke up thinking I was dreaming. My shorts had been pulled down to my knees and I could feel a warm mouth round my cock, licking and sucking me as it hardened. I kept quiet but when my eyes adjusted to the dim light I couldn't believe what I saw, it was a completely naked Emma who was sucking me.
Once I was fully hard she straddled me, guided my cock to her pussy then slowly lowered herself onto my cock and began to ride me. I wasn't that confident with women. The few I had asked out said no so until that point I was a virgin and it was more wonderful being inside a warm wet pussy than I had imagined. Emma fucked me at a pretty furious pace, she rubbed her clit and I felt her tighten then she slumped forward, still shaking from her orgasm and caught her breath as she laid on my shoulder. I was close and it only took a couple of thrusts up into her and I almost blacked out I came so hard, pulsing my cum into a woman for the very first time.
I was in lust, the feeling of pleasure and afterglow Emma had given me made me want to worship her, to kiss her nipples that were pressed into my chest but she was sound asleep, my softening cock still inside her.
As I began to wonder how I'd wake her though, Mom and Dad walked into the room almost in a panic, when they seen Emma naked on top of me, our cum still dribbling from her pussy, Mom gasped, Dad just said 'Oh fuck'. I felt like a deer in headlights, I wanted the couch to just swallow me whole, the guilt of the incest I'd just committed now burning away the pleasure I'd been feeling.
"Son, help me get her up so I can get her into her bed," Said my Dad quietly.
I helped Dad get her into his arms, thankful she was petite and I pulled up my shorts once he carried her to her room. Mom told me to help her clean our mess on the couch with a damp cloth then had me sit on the chair. I couldn't look at her.
"You okay?" Said Dad when he got back.
"I... I didn't mean to, I fell asleep on the couch and it just happened, she didn't even ask me." I said, tears welling up in my eyes.
"It's my fault, I dozed off out here and forgot to lock her door. You're not in trouble Son but there's something you need to know. Emma is probably going to be pissed but you're not to blame." Said Mom.
"I just had sex with my own sister, how am I not in trouble?" I replied.
"Son, your sister has a pretty extreme form of sleepwalking. We've been to doctors, psychologists and even a hypnotist but nothing seems to work. We tried chastity devices but she hurt herself trying to pull them off so now we just lock her in her room at night, she masturbates with her toys instead and goes back to sleep. When she can get out though she'll take whatever man is here," replied Dad.
"Will she remember what happened?" I asked.
"Yes and no, she'll know she's had sex but won't remember who with. Go shower and get some sleep, we'll talk with her and tell her in the morning okay?" Said Mom.
"I uh, it was my first time." I said then left.
I took ages to get to sleep, my mind was reeling about what had happened. I'd fantasized about fucking Emma plenty of times but like the incest porn I watched, it was something wrong to get me off and I never imagined actually doing it. I woke up pretty late, almost jumped out my skin when I woke to Emma sitting on my bed.
"Holy fuck, about gave me a heart attack. How long have you been sitting there?" I said, thankful I was wearing boxers.
"Just a few minutes. You okay?" She replied quietly.
"I'm fine, just got a fright is all."
"I meant about last night."
