My twin sister and I were gifted a week at an all-inclusive resort for our graduation from High School. Being twins we were almost identical except I am male and she is female, so we kind of just kept to ourselves in High School. We had friends of course but we really wanted to spend a week together just us as we got ready to start our lives separate from each other for the first time since she was alone in the world for 8 minutes. We were both going to different colleges so it was important to us to have one final twin outing on our own. 

We were very close Tiffany and I, much more like best friends than brother and sister. She would tell me about her boyfriends and I would tell her about my girlfriends. She would walk into our shared bathroom in just shirt and panties. It was perfectly natural to us. As far as I could tell there was no sexual tension between us whatsoever. 

The day we arrived was horrible. Our flight was delayed and we did not get into the resort until 11:00 PM. We were tired but wired at the same time. But there was nothing to do. So Tiff went to the living room to watch TV and explore our suite. I went to my bedroom to unpack and settle in because I wanted to get up early and go for a run. 

I had just pulled off my clothes down to my boxers to get some sleep, when Tiff burst into my room and said, “OMG you have to come to my room and see this.”

“What I replied. I want to get some sleep.” I replied.

“Just come on it will be worth it I promise,” she retorted and grabbed my arm yanking me up. When we get to her room the lights are off but she pulls me to the private balcony she has. She shushed me and pointed to an open area in the walking path that went behind our building. Silhouetted in the light were two figures. One was squatted down in front of the other head bobbing. Obviously giving a blowjob. I was stunned and immediately turned on. 

Tiff whispered, “See I told you it would be worth it.”

I just nodded. Tiff leaned against the rail of the balcony to get more comfortable. I was transfixed watching this open display of sexuality. My cock was tenting my boxers. And I could feel the lust rising within me. 

I looked at my sister and noticed her butt sticking out from under her night shirt. It was bare. My voice was shaking, “Tiff are you not wearing panties.”

She looked back at me and I swear she glanced at my crotch and saw that my dick was hard and poking out the hole in my boxers. “No silly. It is a thong,” she said while pulling the hem of her shirt up to reveal a red mesh with black ribbon thong.

I gulped. I want to state again up to this point I had never thought or look at my twin sister in a sexual way, but at that moment I was a teenage boy with a cute ass in a thong on front of me. 

She began rubbing my left cheek, “I started wearing them about three months ago. I love the way my naked cheek feels rubbing against my clothes. Or if I wear a skirt feeling the air blow across my ass feels sooo good,” she elongated the last two words in a way I am not sure I have ever heard before in my life. 

We both turned our attention back to the couple on the ground. They had moved the figure that was kneeling was now standing up right leaned over hands on the ground. The other figure was pounding into his partner from behind. Tiff moaned and I glanced and saw motion between her legs.

I croaked again, “Tiff what are you doing. That isn’t right.” 

“It’s ok little brother. As long as we don’t touch it is fine. I know you want to jerk off. It is ok. I want to feel what they are feeling right now. Please stroke your dick while I rub my pussy. As long as we don’t touch it is ok.”

She repeated that same mantra a couple more times I am certain it was to convince herself as much as it was me. I began stroking slowly uneasy about the whole situation. 

I tried to keep my eyes fixed on in the yard but it was not working as my sister was masturbating right next to me. As the lust grew in me my stroking got bolder. I could hear the faint sound of my fingers rubbing her wet pussy. As I was watching her hand under her thong, she moaned and I looked her in the eyes, “Stand behind me,” she breathed.

Lost in the situation I stood behind her and felt her other hand pull me closer and my cock and hand was on her ass. She continued to rub herself and I could feel her body moving underneath me so I began my stroking again. Her hand kept brushing against my balls. It was sending shock waves through me and I knew it would not be long now. I looked up and our mystery couple was gone, but I do not think either she or I cared at this moment. 

Finally I grunted and began to shot rope and rope of cum onto my sisters ass. I lost count after five spurts but I know the fabric of her thong was soaked in my juices. Every time a spurt landed on Tiff she moaned. I was panting and stroking completely lost in the moment. Until finally there was no more. 

That is when reality hit me like a ton of bricks. I looked down and my sisters cum covered ass and panicked. I stepped back and before I realized what I was in my room with the door shut. My heart was pounding. I was scared, angry, and excited all at the same time. I honestly thought I might explode from all the emotions. 

There was a knock on the door and I just about came out of my skin. Tiff walked in carrying her soaked thong in her hand. She walked up to me pushed me onto the bed and said, “You are not getting away with cumming on me so easy.” She straddled my stomach and began to rub her pussy. She evidently had her mind set on one thing because it was not too long before I felt her wetness on my stomach and she screamed out and moaned a loud, “FUCK!!”

She got up looked at the puddle of her juices on my stomach and smiled. She looked me in the eyes and said, “Good night.” She walked out and I watched her ass bounce as it just peeked out from under the hem of her shirt. 

One would think I would not have slept but the day exhausted me along with the emotional exhaustion of jerking off with my sister, I quickly feel asleep.