I live with my parents and two sisters, Kelly who is 6 and Ria who is 13. Ria is hot and I had began to check her out last year as she developed boobs and a cute butt, sometimes I took her panties and jerked in them, they were usually wet and sticky from her pussy. Christmas day we got up and opened our presents, one of Ria's was a pair of white silky panties from her friend and my cock sprung up in my sleep shorts as I thought of her wearing them. That afternoon after dinner my parents fell asleep on the sofa, Ria and Kelly were sat on the floor playing a game Kelly had been given. It was this rubber thing with little knobs on it that vibrated all round this plastic dish and shook off fleas that you had to pick up with tweezer things, first one to get all the colours was the winner, I thought it was sad but Kelly liked it and giggled away. As I looked at them I noticed Ria sitting cross legged, her micro denim skirt had ridden right up and bingo, she had her new silky panties on. My cock instantly went hard as I peeked a look between her thighs, as she moved about the material stretched across her mound showing her pussy bulging beneath and I wondered how juicy it was. My cock throbbed and after a while I snook off and went to the bathroom to jerk off thinking of my sisters cute pussy beneath those silky panties.
Later that night after more food and watching boring TV, mum and dad went to bed, Kelly had already gone, about eleven I went to my room and surfed my laptop. A while later I got up and went into the hall to go to the kitchen to get a drink and noticed the flickering light of the TV still on in the lounge. I thought Ria had fallen asleep so I crept up and looked round the door. As I looked in I saw her lying in the corner of the sofa with her back to me, she had her vest and bra pulled up and was squeezing her nipple with one hand, the other was between her wide spread legs and moving slowly. I almost passed out at what I saw and my cock instantly went raging hard. As I peeked at her I saw her rubbing and squeezing her milky white boobs, her nipples were massive and poking right up. Her thighs were wide apart, she had great thighs, slim and firm, then I noticed she had something orange in her hand and I realised it was the vibrating rubber toy from my sisters game, she was using it as a vibrator. To my joy she still had those white silk panties on and she was grinding the toy into her crotch and slowly rubbing it over the material, I could hear her quietly gasping and the toy making a humming sound. My cock throbbed and twitched as I watched her writhing on the sofa, her hips rising and falling and her firm thighs slowly opening and closing. I couldn't stand it anymore and I crept back to my room, my cock straining hard against my shorts. Suddenly I heard Ria moving about and knowing she would come in I dived on my bed on my front to hide my erection. Moments later she came in to say goodnight, she smacked me on the bum and jokingly said not to jerk off too much to the porn.
I heard her go to the bathroom and then into her room, a few moments later she clicked her light off and only then could I get up and ease the pressure off my rock hard cock. As I remembered what I had just seen my cock almost exploded and then I had a thought. Had my sister put her dirty washing in the hamper in the bathroom? Shaking with excitment and nerves I padded along to the bathroom, my cock standing up and twitching. I quietly closed the door and clicked on the small light, lifting the lid off sure enough she had put her washing in the hamper. As I picked off her skirt and shirt, there were her panties, the leg bits rolled around. I picked them up and felt they were still warm, the crotch was wet and sticky all over from her cum and juice and smelled of her. I placed the damp crotch over my throbbing cock and un rolled the rest of the panties, they hung off my jerking cock which was throbbing with my heart beat. I was sure I could make out the shape of my sisters pussy still in the warm silky folds as I slowly stroked it over my cock. Moments later I exploded and my whole body jerked as I shot great gobs of hot sperm into the soft silky crotch, my twitching cock rubbing against the fabric that had rubbed my sisters horny pussy to orgasm. I used the back part of the panties to clean my cock and then put them back under her other clothes. Watching my sister masturbate has been the horniest thing I have seen so far.