This happened about a little over a year ago in the summer. Our mom and dad worked all day long so I was left all day long at home with my sister I’ll call her Cindy. she was about 5 feet nothing tall,acute curvy ass, small round little b cup tits topped with large nipples about 100lbs long blonde hair.
Our parents had already left for work and I had just gotten up and had to go use the the bathroom. Sitting on the toilet I could look into the backyard from the second floor window and see the whole backyard and tool/storage shed. I heard the back door close and and Cindy trotted across the yard in a pair of shorts and t-shirt with king the family dog a large male German shepherd along with her to the shed when she got there she looked back towards the house acting sneakily. Opening the door king went right in my sister looked all around and closed the door behind her. I thought that was very funny and decided to go take a look at what she was doing. Putting my phone in my pocket I hurried downstairs and to the shed.I looked through the window Cindy was laying back on a old upholstered chair with her ass off the end and king was licking her pussy as she held onto his head I could hear her moaning. I got my phone out and started video taping her and the dog. I got about a minute or so before she let go of his head and motioned for him to jump up putting his front paws on either side of her chest he started humping right away stabbing around, she reached down and guided his pink cock into her pussy missionary style. King hunched over and pounded away at her like a jackhammer as she moaned louder and louder. After a couple minutes he slowed down as Cindy wrapped her legs around him. At that point I walked in saying something like wait til everyone sees this, Cindy looked at me terrified and begged me not to tell that she would do anything. I dropped my shorts and told her to let the dog go because I’m next. She said I can’t he’s stuck, I now remembered when he had knotted one of the neighbors bitches and how upset that Cindy became when I showed her. I walked over with my 7 and half inch cock sticking straight out and grabbed her head and started face fucking she gagged spat my cock out as she turned her head struggling saying not so hard. I told her to make me cum.I stuck my cock back up to her lips and she opened her mouth and started to Bob her head back and forth faster and faster for a couple of minutes I moaned loudly as I shot several streams down the back of her throat she swallowed it all and kept sucking till I pulled back. I sat down next to her and asked her how long had she been fucking king. She said for awhile that it was better than masturbating. After that king pulled out of her .I watched as his cum poured out of her pussy.she got up and went to the house with me following her into her room she hadn’t put her shorts back on as I put my arms around her grabbing her tits pinching her hardening nipples through the thin material of her shirt. I pressed my stiffening cock against her back as I pushed her over the edge of her bed. I rubbed my cock up and down her slit finding her slick hole I slammed it all the way in and grabbed her hips pumping her almost as fast as the dog. She was soon moaning her delight and yelling fuck me harder Ricky and as I could feel my orgasm building she cried out I’m coming I slammed in as hard as I could and shot several more streams of cum into her. When I finally pulled out she said that was the best sex she ever had. She said if I ever told anyone that I fucked her that it would be the last time. Needless to say that we can’t wait til our parents go to work or get home from school so we can have sex. I ain’t gonna tell no one.