My little sister is a senior in high school, but she definitely still doesn't look or seem like an adult to me. She has always been a homebody, spending most of her time hanging out with my parents or reading books. She is barely five feet tall and weighs maybe 100 pounds. She has a cute face, I guess, but never wears makeup or dresses to look attractive. Her wardrobe is basically the same as it was in middle school. I couldn't even tell you her bra size, because she doesn't really need to wear them, and on the rare occasion she does it's a sports bra. Never in my life have I thought of her as being more than my kid sister. She is naive to almost everything worldly and as innocent as they come.
I'm five years older than she is, and we have never really spent much time together. Last weekend I was in my hometown to visit, sleeping on the couch for the weekend since my room had been converted into an exercise room by my dad pretty much right after I moved out.
The first night I was there our whole family sat down in the den, which is where I was sleeping, to watch a movie. It was a corny romantic comedy that didn't really hold my attention. I spent most of the movie looking through my phone, aside from telling my parents to "get a room" annoyedly several times. They are almost annoyingly happy together, and they kept smacking kisses and cuddling on the couch opposite of the one my sister and I were sharing.
Right when the movie ended, they retired for the night, leaving my sister, Alyssa, and I to find something to watch. After a few minutes of searching, she decided on some subtitled foreign film on Netflix. I paid little attention except for when I noticed a pretty raunchy sex scene about five minutes into the movie. I looked at Alyssa puzzlingly, surprised she would be interested in the weirdly graphic eroticism on screen.
"Fake news!" I blurted out jokingly.
"What's fake?" she asked.
"Probably the whole thing," I said. "Fake story, fake sex, and my guess is those are fake tits," I told her as the actress bounced up and down making ridiculous moaning noises.
"Sorry, I didn't know it was like this," she replied. "Plus, don't guys like big boobs?"
"Well, yeah, kind of," I said. "But not those fake ones. I prefer natural tits, even if they're small."
"Well no one else seems to like them," she pouted.
"No offense, Alyssa, but you don't even really have small boobs yet. More like a flat chest!"
She didn't reply.
"That's not all that's fake though. The way they're moaning sounds like a bad porno. Not realistic." I got up to grab a beer from the fridge, and she paused the movie.
As I walked out of the den I heard some pounding down the hall. I listened closer and could hear very clearly my parents were having sex.
"Maybe I was wrong! Come here!" I whispered to her. She got up and followed me quietly down the hall by my parent's closed bedroom door. From where we stood, we could hear the obvious sounds of passionate sex on the other side of the door. Alyssa looked at me in shock with a smile on her face. It was kind of funny at first. Then I unexpectedly started feeling turned on by what I was hearing.
I quietly motioned for her to follow me outside and we went around the house to look in their window. Through the blinds, we could see my mom naked spread eagle as my dad ate her out. My mom didn't have big boobs either and as she lay flat they looked even smaller.
Alyssa looked at me and said, "Mom's boobs look just like mine, don't they?"
I was caught off guard because I was getting a boner watching my mom getting eaten out. "Wait, what did you say?" I asked my sister.
"My boobs are just as big as hers," she said.
"Prove it," I said, not realizing how fucked up that sounded until it was already out of my mouth.
I looked at Alyssa and gazed at her chest. Whether from the cold or the arousal of watching our parents fuck, her nipples were poking out prominently, and for the first time in my life, I wondered what they looked like. "You do have some pretty pointy nipples, but I've never seen your boobs so I couldn't tell you," I said.
She just stared at me. By now I was super horny and for some reason, I just slid my hand up her shirt and felt her tiny breasts with both hands and pinched her nipples. She cooed and laughed and I told her they were acceptable. We focused back on our parents, and my dad was taking his pants off. He was obviously hard, and my sister gasped when she saw his cock. He drove it inside my mom's pussy and started pumping.
Alyssa was up against the window and as I stood behind her I reached under her shirt and played with her nipples again. My parents were fucking doggy style and she couldn't take her eyes off them. My cock was rock hard in my pants and as I moved closer behind Alyssa I knew she could feel my boner.
"This is better than the movie," she said under her breath.
I moved closer, basically pinning her against the siding with my crotch on her butt, and my hands on her tiny boobs. I was so horny I slid one of my hands down her torso and under the seam of her panties. She turned around in surprise as I touched her clit. I kept watching my mom and dad and slid my finger inside Alyssa's soaking pussy as I grinded against her. She pressed her ass back against me and I bucked her hard against the wall.
I got on my knees and pulled her pajama pants down from behind and used my fingers to play with her pussy from the back. She didn't say a word but continued watching my dad give it to my mom. With half my attention watching the show inside my parent's bedroom, I pulled my pants down and guided my cock inside my little sister. I covered her mouth with my hand and fucked her hard against the side of the house until she came, tightening her pussy around my cock. I slowly regained my pace and pumped her until I came inside her.
She had another orgasm as I emptied myself and her hand that had been gripping the siding slipped and landed on the window to my parents' bedroom. They both looked over immediately, then my dad stood up and walked towards the window and we were caught red handed. He saw both of us watching through the window. Fortunately, from his angle, he couldn't tell I was balls deep in his only daughter.
We snuck off and tried to get back inside, but were met at the door by my dad, covered only by a bedsheet he grabbed on his way out the bedroom. Alyssa and I were sweating, clearly aroused, and I expected him to freak out. To my surprise, he just said, "follow me."