My sister, Ethel, is a widow and lives in a town about twenty miles from mine. She came to visit me for a few days and I gave her my spare bedroom to use. We taljked about our lives.
"You`ed never married, Harry. Have you had a live-in girl friend?" she asked.
"No, I haven`t".
"You are twenty two and still a cock virgin. You must get an urge sometimes. What do you do about it?".
"I watch blue films on my computer in the nude. They get me worked up".
"That means you get an erection. Do you masturbate then to get rid of the urge?".
"Yes, I do".
"I`ve never seen a blue film, Harry. Can you show me one?"
I took her to my computer room and turned on my lap top and obtained a sex film. I was fully dressed but the effect on me was shown by the bulge in my trousers.
"I can see what you meant when you said you got worked up, I can see a swelling in your trousers. You said that you watch films in the nude so why not undress?".
"In front of you, Ethel?".
"Why not? I won`t mind. I`ve seen a little of that film and I`m a little worked up, too. I`d love to see you naked and masturbating".
"I`ll do it but you should undress, too".
I ran the film back to its` start and put it on hold then we returned to my lounge and undressed. I`d never before seen my sister naked and I liked what I saw. So much so that my cock, which had softend a little, swelled up again. Seeing her in the flesh was much better than seeing a naked girl on my computer screen. In fact my sister was the first naked girl I`d seen.
Both naked, we went back to my computer and I restarted the film. The first part showed a naked man and naked girl caressing each other. She stroked his cock to full erection and it was huge. He pushed fingers into her shaven pussy. Then another naked man joined the naked couple and the girl stroked him to full hard-on. It was huge, also.
The first man fucked the girl, followed by the second.
"My word, Harry. The girl has been done by two men, one after the other. I want to masturbate you and you to masturbate me.

I`ll hold your cock like the girl in the film did with the men and you put your fingers into me as the men did with the girl. You`ve never done that before with a girl but I`ll tell you what to do".
Ethel stood in front of me and I put some fingers into her cunt. Then she told me to feel for something in there. I felt something and she said it was her clit and I should caress it. When I did it became quite hard. She told me to continue caressing it then held my hard prick. We masturbated each other for a short while.
"This is silly, Harry. We are masturbating each other but I want you to put that big erection into me as the men in the film did with the girl".
"If I do it will be the first time I`ve had sex. I want to fuck you now you`ve got my dick right up. I`ll do it".
"I`ll lie down on my back on the floor and we will do it there".
Although I`d not fucked a girl I knew what to do because I`d seen it done in sex films. I shot my cum into my sister and gave her four orgasms before I withdrew. It was incest of course but we didn`t care.
"You did well for your first sex, It was the size of your cock that made it so good for me. How was it for you?".
"Wonderful. No wonder those men in the film seemed to be enjoying fucking that girl".
"Let`s do it again tomorrow, Harry".
We dresswd and Ethel asked me to show her how to get blue films on her computer when she returned home.
I took a lot of trouble to explain to her what to do and I wrote it out for her to be sure that she could do it.
We fucked twice more before she had to return home. After a day or two she telephoned to say that she had set up her computer, was watching a sex film, and was naked. I wasn`t but quickly stripped off and told her whan I was naked. We decided we would masturbate ourselves and told each other what was happening to ourselves, step by step. I told her I was cumming and enjoying it and she told me, between gasps, each time she had an orgasm.