Incest Brother/sister Anal Sex 'This is a work of fiction. The author does not condone any sexual activity among persons under 16 in real life. Back Door Sis by GEMINIGUY "The men don't know/But their little girls/ Understand..." *************** "Hey, Jimmy -" My sister, Cassie started as she barged in my bed room but stopped with a gasp. I was laying on my bed jerking off when she'd just opened my door and walked in. If you feel like you walked in the middle of the story, let me back up a bit. I live in California, I'd graduated from college 2 years ago. I worked part time as a lifeguard through college [actually since I was 16] but I haven't been able to get a job in my field yet so lately I've been working more hours at the beach. I'm a pretty buff guy, work out as much as I can and obviously I have a great tan. You'd think I'd be getting laid like crazy but not so. I pick up a hot babe now and then but never anything steady. Recently my parents called me to get me to come watch my sister for 2 weeks while they vacationed in Japan. I have a small place so it would be nice to 'stretch out' for a while I thought to myself. They only live an hour away from me. I drove up the evening before they were leaving and sacked out in my old room. They'd left it just the way it way. My parents have their own bathroom but if either Cassie or I need to use the bathroom we have to go downstairs. It must have been a little after midnight when I went down to take a leak and on my way up I had to pass mom and dad's bed room. I heard giggling coming from their room. I know my parents are still sexually active; mom's 44 and hotter than the girls my age, and dad is 48 and he works out as much as me. I heard mom gasp and giggle "What are you doing?" Curiosity got the best of me and I knelt down to peek through the keyhole [my parents lived in the same house dad's parents did so it's a pretty old house with most of the original old fashioned features]. I immediately began to get hard. Dad had mom on all fours, her perfect butt to me. "You know perfectly well what I'm doing..." Dad replied to mom. He was reaching into the drawer of his nightstand and pulled out a jar of Vaseline. He stuck 2 fingers in and scooped some out and smeared it up mom's dark-haired butt cracked. Mom moaned. Then dad slid I finger up mom's butt hole! Mom moaned. The fingered mom for a while before adding a second finger. Mom was rocking back and forth and his finger and she came before dad pulled out. He coated his cock with Vaseline and guided it to mom's butt hole. I pushed the head in and mom gasped louder. By now I had my cock out of my boxers [good thing Cassie's room is at the back of the house and she uses the back stairs to get down to the bathroom] and was stroking off. Dad had turned mom sideways so now I could see her double D's dangling down, her big brown nipples rock hard surrounded huge areolae. They swung back and forth as dad butt fucked mom until he reached under her and grabbed them. He kneaded them as mom came again. She kept moaning for dad to fuck her hard. He planned into mom harder and she sobbed as she orgasmed again. Mom came like 6 more times before dad grunted he was about to cum. After he shot his load mom pulled off of him and spun around. She took his slimy cock and in her mouth and sucked it clean, moaning the whole time. I watched wide-eyed as my mom was able to deep throat dad's cock and it was almost as long as mine but not as thick. I knew I was about to cum myself so I ran to my room down the carpeted hall. I shut my door and threw myself on my bed. I stroked faster and grunted. The first gusher of stringy white jizz flew from my cock almost halfway to the ceiling. The next 3 blasts almost as high, the last 3 just splattered on my stomach. I gasped for breath as I laid there temporarily sated. I soon fell asleep fitfully. My alarm woke me early the next morning. I had to drive mom and dad to the airport. I couldn't help staying half hard around mom. I was seeing her a new light; I'd known she was hot but I'd never been turned on by her before. After dropping them off I drove their station wagon back home and grabbed Cassie and we drove in my car down to my beach. I had a shift to pull and sis was excited to get to go to the beach. She had a pool at school and sometimes swam in a friend's pool but never got to go to the beach. Cassie positioned herself close to my tower. She slid out of her shorts and top, revealing a cute bikini that wasn't in itself revealing for her 13 year old body but it made her womanly butt and breasts under it obvious. Cassie had some 'meat on her bones' and was sporting a pair of D-cups already. I could tell she'd have a body like mom's but Cassie is short and I don't think she'll have mom's height. I kept an eye on sis but she didn't distract from my job. Or from the babes. I couldn't help comparing them to mom; and whenever one bent over near me I nearly blew my load. I had to go in my tower several times to rub off a few to make it through the day. After I took Cassie by my place so she could see it [it only has 2 rooms (my bed room and the kitchen/living room) and a decent-sized bathroom] then I took her to my favorite pizza place. Back at my parents' house we watched re-runs of our favorite prime time shows [no good new shows during the summer] and went to bed at 11. I took a quick shower and Cassie went in after me. I was laying in bed thinking about mom getting butt fucked again and got instantly hard. I started whacking off and that was when sis had walked in on me. She was blushing but didn't back out of the room. I slowed down my stroking but I found myself not stopping. Finally I asked "What did you want, sis?" Cassie blinked and blushed darker. "I don't remember..." She admitted. "Ummm, Jimmy... What are you doing?" I was surprised Cassie didn't know. We'd always been open with each other so I told her right out "I'm masturbating." "Oh. Why?" "Because it feels good." "Why is it hard like that? I saw daddy's once but it was soft." "It gets hard when I get turned on." "Oh, like by one of those women in the tiny bikinis on the beach today?" "Yeah," I said. Talking to Cassie like this was making me hornier... I was starting to see my sister in a new light, too. She was very pretty and sexy in her own way. I decided to tell her the truth and see where things went. "But I was remembering something I saw last night. I saw mom and dad have sex." Cassie's eyes went wide. "You - you did?" I nodded. "Yeah, but he wasn't having regular sex; his penis wasn't in her vagina. Dad had it in mom's butt." Sis gasped. I was looking at her in her short nightgown. I wondered if she was naked underneath... "I was thinking about what it would be like to do that to mom..." "I heard that's wrong, isn't it?" "Some people say it is, but that's why you don't tell people if you do think about stuff like that. Hey, sis..." "What?" "I have been noticing how pretty you've become. Even sexy." Cassie blushed. "Thank you..." I smiled. "Sis, how about you let me do that to you, what dad did to mom?" Her eyes went wide again. "B - but... You... Wouldn't it hurt?" "No," I answered. I opened my nightstand drawer and pulled out a tube of vaseline. "Dad put this up my mom's butt and on his penis first. It makes it easier to go in." Cassie looked at it then nodded. "Okay. I've never done anything with a boy before and I'd like to try. What do you want me to do?" I told sis to undress. She nodded again and shut my door. She grabbed the hem of her nightgown and pulled it over her head. Cassie had on grey cotton panties and a matching bra. Dropping her gown on the floor she reached back and undid her bra. She slid it off and her tits came into view. Cassie had light brown nipples surrounded by medium-sized areolae, almost oval-shaped. Her nipples were hard but not that thick. Cassie reached for her panties and slid her fingers under the waistband. She slowly pushed them down. Her brown pubes came into view. Sis had a lot of hair down there but I'd seen thicker bushes. Cassie looked at me - hands cupped over her bush - and asked what now. I told her to get up on my bed on her hands and knees, her butt towards me. She did, then wiggled her butt and giggled. Imitating dad, I smeared some Vaseline on my fingers and rubbed it into my sister's crack like he'd done to mom. Then I slid a finger up sis' butt. She stiffened and moaned. I slid it in and out and Cassie couldn't stay still. I added a second finger and opened sis more. Cassie came while I fingered her butt. "What was that?!?" "Seems you had your first orgasm, sis." "Oh." I pulled my fingers out and smeared Vaseline all over my cock. I took hold of it and guided it to sis' butt... "Are you sure it won't hurt?" Cassie asked, looking back at me. "Mom loved it when dad did it." She nodded. I pressed the head of my cock against her butt hole. I gently pushed forward and the head popped in. "Oh!" Cassie gasped. "Are you all right?" "Yeah," She giggled. "I'm just not used to the intrusion." I put my hands on her hips and pressed forward. A few more inches slid in. Cassie moaned. She was breathing heavy now. I slid in further. It took me a while but I got every inch up her butt and sis came again before I did. I let go of her hips and I leaned against her and grabbed her tits. "Oh!" Cassie gasped then giggled. Her nipples got harder against my palms as I kneaded her tits. She was moaning and as her body relaxed under me I noticed her butt loosened up. I started sawing in and out of sis. She moaned louder. I had never realized fucking a butt would feel so different, be this tight... Cassie came again before I got a rhythm going. Soon I was pounding in and out of my sister's butt and she was begging me not to stop. I didn't, even after Cassie came 4 more times and I blasted her insides with my jizz I kept fucking my sister. I lasted longer the second time and Cassie came another 8 times. We collapse side-by-side on my bed, my cock still buried up sis' butt. She sighed as she drifted off to sleep. As I drifted off myself I thought about how much fun the next 2 weeks were going to be... THE END