When I was younger, about thirteen, me, my sister, and my one year younger female cousin used to play a sort of masturbation game. It was held in my room, which had a lock on the door, and we usually only played late at night or when everyone was at the store except us.
We made a board for it, dice, and cards-pretty much a regular board game. The cards would say things like 'Lick the person to your right's tities', 'Hump the side of the chair naked', or 'Keep your hands on your clit till your next turn, but no orgasming.' It went on for a few years until my cousin moved away.
I had always been really attracted to my younger cousin, and really loved it when I got to do things to her during the game. When I got to see her humping up against the side of the bed, or touching herself, I felt really horny.
On one occasion, I had drawn one of the more dirty cards out of the stack, 'To the person on your right-hump her from behind and finger her while she massages her tities.' Of course, I was really excited. It was one of the cards I had written out specifically with her in mind.
When we had both taken off our clothes and gotten onto the bed, I was extremely horny. After weeks of the game, I had never gotten to finger my sister or my cousin, just myself, and I was slightly worried I might mess up. But when I got on top and brought my hands underneath her, she began thrusting into them and touching her tities like the card said.
Humping her upper leg, I started rubbing my fingers against her clit and we were both panting hard in a sort of rhythm. My sister was watching us, and I could hear her panting, probably touching herself too. The feeling of my cousin's leg between mine was really hot to me, and I humped her faster and faster, keeping my fingers going at the same pace, making her moan quietly.
We both came pretty quickly, being twelve and thirteen.