I pull from my own experience, things that happened.
My wonderful sister is a couple of years younger than I. We were both swimmers although later on I was interested in other sports like football. I left the violence when I could; she went to nursing school and left later.
She was husky, had short brown hair, and was about 5'7". I came to visit her apartment, and she wanted me to stay for a few days. We sat on the couch talking, and she told me she wasn't seeing anyone and was really lonely. There were people from work, but she couldn't approach anyone there since it was a hospital. I'm a loving brother so she got lots of hugs. She invited me to a different apartment complex where people from her work were, and their friends.
But, she said, I had to pretend to be her boyfriend. I grew up in the same wreckage of a home as she did so I also never gained social skills and have no girlfriend. We went, and I drifted around and looked at the girls in the pool. My sister kept coming to me and grabbing my hand. She finally pulled me to the side and was mad at me. She said I'm supposed to be her boyfriend and I'm acting like a brother. So she ordered me to kiss her. I kissed her. NO! 'I want a real kiss'.
I kissed a little better. It still wasn't enough, so she put her hands on my butt, pulled me very close, and we started really kissing. I started to get hard, and I was thinking this is really nice. I really enjoyed kissing her, even though she was my sister. So I put my hands on her butt and pulled her even closer. I was really hard by now and pushing into her. I know she could feel it, she was thrusting right back at me. I really liked this. We pulled apart and went back to the group. She didn't know most of them but wanted to meet guys. These were people known to the people she worked with; she wasn't interested in dating anyone from work.