It was 7 pm and the office was empty and the floor was much in dark. I starting walking towards the men's room and realize that my sister is following me. At first I thought she had to go to the ladies room which is next to the men's room but when she stood right behind me as I opened the men's room door I realize what she had in mind. She smiled at me and followed me right in. I was nervous a bit. I walked into a stall and she followed me in and shut the door behind her. We just stood there for 30 seconds until I whispered "what shall we do?" She replied by moving closer to me and kissing me on the cheeks. I put my hand in the back of her head and kissed her lips. I kissed her with my tongue deep next thing I know my sister got her hands on my cock rubbing it through my pants. I could not take it anymore and had to feel my sister's gorgeous round ass. I put my both hands onto her butt cheeks and started to massage them and pull her into me. The passion heated and my sister removed her hands from my crotch and allowed me to pull her into my crotch. I could feel her wet warm mound rubbing against my bulging huge cock.
After about 10 minutes grinding and dry humping each other my sister pushed me against the wall and started gyrating her pussy against my huge cock. In two minutes she started to shudder and cum which put me over the edge and I came in my boxers. We both quietly kissed each other and walked out of the bathroom.
This went on for a couple days. We would go in the bathroom, get all worked up, grinding against each other until we both would cum hard. Third night my sister took my cock out of my pants and started stroking it until I came. Once I went limp she got down on her knees and started sucking my cock and massaging my balls. Immediately I got hard and came in her mouth. I had to return the favor. I got down on my knees, opened her jeans from the front, slid it down to her knees along with her moist panties and shoved my tongue inside her pussy. I started chewing and sucking on her clitty and sliding my tongue in and out of your sweet horny wet warm pussy. I felt her hand grab my hair pull my face into her sexy cunt until she came multiple times drenching my face with her sweet pussy juices. I got up we got dressed and left the bathroom.