This happened a couple of years ago. I was 16 and my sister Grace was 13.
That summer was the first summer that my parents didn't send my sister Grace to a babysitter or summer camp for middle school kids. They said that she was old enough to stay home with me while our parents were at work all day. I wasn't too happy about this because Grace was the typical bratty little sister. She hadn't really matured very much yet and my parents favored her all the time since she was their baby and their little girl.
For practically the first month that school was out, we kept to ourselves. I watched TV in my room and screwed around on my computer while she talked on the phone with her friends or watched movies on demand in our living room. The only time we really talked was at lunch, when we had lunch together. Often she would just make herself a sandwich and I would simply munch on chips and cookies all afternoon. Grace would wake up much earlier than I did, so I didn't know what she was doing while I was asleep.
One morning, I woke up at 9:00, early for me since I usually slept till noon or 1:00 and I stumbled into the bathroom to piss. I was still in a fog of sleep. As I was making my way downstairs, I heard Grace watching cartoons in the living room. I asked her how long she had been up and she said since 3am and that she was actually about to go take a nap. I went on into the kitchen and ate some pop tarts. Grace turned off the TV and went upstairs. After my pop tart I turned on the TV in the living room and got an on demand movie. I forget what movie it was, but about half way into it there was a really steamy sex scene. I got hard watching it and I stayed hard the rest of the way through the movie. When the movie was over, I was still hard. I listened for Grace but I heard no noise coming from upstairs. So I decided I would get a porno on demand. My parents never noticed when my friends and I ordered them from the TV in my room, so I knew they wouldn't notice now either.
So I started watching the porno with the volume fairly low as to not disturb Grace. I picked one I had watched before with a friend of mine with a girl giving a guy head and then the guy having a threesome with that girl and another girl. I slid my pj bottoms down to about my knees and my dick stood straight up. I began to slowly stroke it. I spit on my hand for some lube and it felt even better. I continued to slowly jerk off watching the porno. I was just about to start jerking more vigorously when I heard Grace come bounding down the stairs. I quickly pulled my pants up and reached for the remote to stop the porno. She rounded the corner into the living room right as I picked up the remote. I quickly paused the porno. I meant to stop it but I had hit pause instead. Grace's eyes got really big and she gasped and covered her mouth.
'I know what you're doing!' She exclaimed.
'No, it isn't what you think.' I defended, trying to sound as innocent as possible.
'Yes it was! You were playing with your DICK!' Grace yelled as she pointed at my hard-on.
'I was just...' I started.
'You were jacking off! Gross!' She shreiked.
'Grace! Shut up, okay? Don't tell mom and dad, okay?' I practically begged.
'Why shouldn't I?' She asked. Typical bratty kid sister.
'Because I wouldn't tell them if I caught you masturbating.' I replied, and I was telling the truth.
'Why would I do that? That's gross!' She continued. 'Only perverts play with themselves!'
'That isn't true.' I argued.
'Well, I'VE never done it!' She announced.
'You should try it.' I said. As I said it, I didn't mean to be suggesting anything, I was only trying to keep her from telling our parents about this.
Her face fell.
'What?' I asked, the last thing I needed was to say something that upset her even more.
'Well, I like, it's just... well...' She didn't know what to say.
'Look, whatever you say, I don't care. I won't tell anyone.' I told her. I was still trying to bargain my way out of her telling on me.
'Well, I lied. I have tried it, and nothing happens!' She said. I couldn't tell if she was more mad or sad.
'You just have to know what you're doing. You have to figure out what you like.' I said. I was getting even more turned on talking to my sister about masturbating.
I have never been attracted to Grace and she, at the time, wasn't very developed at all. She was only in an A cup and she had almost no figure at all. She was straight as a stick and flat as a pancake, but the sheer kinkiness of talking about masturbation with my little sister, it was erotic.
'I mean I think I know what to do, it doesn't sound very complicated.' She said. She sat down next to me on the couch.
'Sound? Who told you about it?' I asked.
'Some girls at school talk about it a lot.' She replied.
'Well, girls at school don't always know what they're talking about.' I told her.
'They kept talking about fingering their pussies, so that's what I did.' She said.
Holy shit, that made my cock twitch in my pants. Hearing the words 'fingering their pussies' coming out of the mouth of my 13 year old sister was amazing.
'You can do other stuff too.' I informed her.
'Like what?' She inquired.
'Like you could hump things, or rub your clit, or do...' she cut me off.
'Rub my clit?' She repeated, confused.
'You don't know what your clit is?' I asked.
She blushed and looked away. Then shook her head.
'It's like, by...' I trailed off.
'No, tell me. I wanna know, I NEED to know!' She stressed the word need.
I started to chicken out.
'Look, I don't know if I can do this. You're my kid sister.' I explained.
'Well, can we pretend I'm not? Just until you teach me? Then we can be siblings again.' She asked, she pleaded.
'I suppose,' I sighed. 'But you cannot tell anyone!' I said.
'I promise, I won't.' She said.
'Okay, it's like by your l...' she cut me off again.
'Can you show me?' She asked.
I was blown away. My sister, who never liked me was asking me to look at her pussy and show her where her clit was.
'Uhm, that's so weird.' I said.
'Please Keith?' She begged.
'Okay, fine.' I agreed.
She pulled her pajama shorts off and laid down on the couch with her crotch facing me. I was staring at her panty clad pussy. She was wearing green panties with little frogs on them.
'Can I take these off?' I asked her. I didn't want to do anything without her permission.
'Yeah,' She said.
I pulled her panties off and tossed them to the floor. I was looking directly at my sister's pussy, I was only a foot or two away from it, and I was about to touch it. There were a few whispy blonde hairs on her mound, but no substantial hair to speak of. Her lips were a light pink color, and looked very soft.
'Go on...' She whispered.
'What do you want me to do?' I asked.
'Touch it.' She instructed. 'Touch my clit.'
So I did. I reached over and parted her lips and softly began to stroke her clit. I did this for about a minute when she spoke again.
'Will you do it for me? Teach me how?' She asked.
'You want me to masturbate you?' I asked, shocked at what my sister was asking me. I was horny as hell by this time. My cock was beginning to ache.
'Yes, do it like you would do for your girlfriend.' She said.
'How do you know I've done this for girls before?' I asked.
'I just know these things, okay? Now do it!' She said.
I went to work. I began to rub her clit in circles. I experimented with applying different amounts of pressure to it as I rubbed. She moaned once slightly and I stayed at that pressure. Then I slowly slid one finger into her tight hole. She gasped. I asked her if it was okay and she said it was fine, and to keep going. I did. I slowly eased a second finger in and she gasped again. This time, before I could even ask she told me to keep going. So I did. Soon I was going full speed with two fingers in her and rubbing her clit in a rhythmic pattern. Grace began breathing fast and writhing around on the couch. Then she let out an ear-piercing groan/scream kinda noise and I felt her vaginal muscles clenching around my fingers in orgasm. She kept wiggling around and finally said 'Oh God! GOD!' And laid back flat on the couch. I stopped and pulled my hand away. It was wet with her juices.
'Oh my God Keith! That was amazing!' She cried.
'You're welcome.' I said, rubbing at my hard-on.
'You can jack off now if you want to.' She told me.
I decided what the hell. So I pulled my pj pants back down and let my cock spring out. It hit my stomach and then stood straight up in front of me. I was only about five inches at the time but Grace still seemed fascinated by it. She started at it like it was going to disappear or something. I began to stroke it slowly as I was earlier. I didn't wanna come too fast. But after only a few minutes, I knew I was close. I could feel my orgasm building in my stomach and balls. Grace was still staring at my cock. I was gonna cum. I moaned and closed my eyes and the first rope of cum shot out and landed on the floor in front of the couch by Grace's shorts and panties. The second rope shot up and landed on my stomach. I opened my eyes to watch Grace lean over as the third rope shot out and hit her on the cheek. The next rope landed on her shirt, and the rest dribbled out and coated my hand and my cock.
'Holy crap, there was a lot!' Grace said, wiping my cum off her face.
'Sorry,' I chuckled.
'It's cool.' She giggled back.
As we sat there, both of us naked from the waist down, we talked about masturbation and sex and everything related to it. We decided that while this was fun, we shouldn't make it a regular occurance. After a few minutes of recovery, I headed to the bathroom to shower and she stayed in the living room until I was done. We went for about a week and a half before we finally decided to, despite what we said, do it again.
For the past year we have been masturbating together and masturbating each other. We have never gone further than that and we don't plan on it. But never say never. Grace has definitly matured physically, she has nearly C cup tits now and a normal tuft of pubes. We still enjoy each other and we try new things and learn new things all the time. It is really great to be able to do it.