This is going to take a while, so please bear with me. Also, English is not my first language, but I will try my best.
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My name is Mark and I am 51 years old, married, with one daughter.
I have a younger sister, Anne, who's 49, married with 3 kids.
When we were... younger, we had played "those" games quite a lot (doctor and patient, king and servant, etc.) but our most favorite one was "Show me!"
One of us would say "show!" and the other would either say "no, you show first" or he/she would just "show": if it was me I would show her my dick and if it was her she would show me her pussy (usually) or her tits.
It had started in one of those plastic inflatable pools we used to play in. We were both curious and we had started showing ourselves to each other and eventually touching as well.
This would slowly progress to us touching each other more often, kissing on the lips a few times and after some time I asked my sister if I could lick her!!
She was shocked and disgusted at first but after my pestering her for a while she gave in. From the very first second my mouth and my tongue touched my sister's pussy I was hooked and I still am to this day (both to her pussy and to giving women oral sex in general)!!
Anne loved it, as well, so it became a regular part of our little "routine". Our favorite position was with her lying face down with her ass high up supported by her knees, legs spread, and me in between them eating her out like a thirsty puppy!! When I was pushing my tongue as deep inside her as it would go, she would also grind her pussy against my face so my tongue would reach even deeper.
I am positive she came every single time we did that. Unfortunately, she never returned the favor and I did not want to press her. Also, we never had fully penetrative sex, although we came pretty close on a few occasions. On one of those, in particular, when we were both very turned on, my sister had already taken her panties off and asked me if I wanted to try and put my cock inside her pussy!! I was shocked and thrilled at the same time and I remember that my hard-on was so big and firm, it was painful.
Almost shaking, I grabbed my dick and guided it towards my sister's gaping and inviting pussy. When the head reached its destination, I slowly pushed and I felt my sister's pussy walls open and then close around my dick, just like a hot, wet, soft hand in a glove!! The feeling was absolutely incredible, out of this world!!
I was almost all the way inside Anne's body when I felt her hand at the lowest part of my torso, just above my cock, pushing me away. I stopped pushing in and I whispered to her:
"Don't you like it?" to which she replied:
"I like it, but it hurts a little."
That must have been her hymen - since she was a virgin, and she continued to be after we had ended our "sessions".
Disappointed, I pulled my cock out of Anne's pussy. She saw my face so she offered for us to play with each other for now and she would try and take me all in next time (that never happened, though).
On another incident, we were in our bedroom after (supposedly) we had gone to bed. The light was off and the door was almost closed, with our parents in the kitchen. Anne had taken her panties off and I had my pajama pants down to my knees. We were standing behind the bedroom door, in the dark, and I was between my sister's legs.
We wanted to simulate the sexual act so I pushed my cock downwards and just under Anne's pussy, grinding the head and the shaft all over her pubic bone and her pussy lips.
We did that for a while and when I put my hand between us I found out there was a LOT of my sister's pussy juice all over my cock - as if my cock had been inside her - and her pussy was completely soaked. It was thrilling but we got scared and jumped back to our beds before our parents caught us.
It was convenient for us, as we had to share a bedroom since our house was small and risky at the same time as our folks' bedroom was just opposite. Whenever we wanted to "play" in the afternoon during spring or summer time (it is quite hot in our area so people usually take afternoon "siestas"), we would go to our bedroom and close the door.
I then would go and check through the keyhole if our parents' bedroom door was closed as well. If it was, the fun would start, but we were always vigilant and listen out for any noise that would mean their door was opening: in that case I would jump straight back to my bed and we would both pretend to be asleep.
We never, ever got caught, by our parents or anyone else. There were a few close calls, but in general no one knew except for us two.
There was a time one summer when some friends had come over and asked if we wanted to go to the beach with them. Anne was more than happy to follow but I had some chores to do (as a punishment from my parents for something - I don't even remember what it was) so I was stuck and could not go.
I was pissed off beyond belief but there was nothing I could do. I could see that my sister felt sorry for me but she couldn't do anything and she didn't want to miss the beach.
Later in the afternoon I had finished my chores and as I was shattered I went to bed for a "siesta". It was very hot so I changed into a pair of shorts and nothing else and instead of our bedroom I went to the living room and crashed on the sofa. Our parents were already in their bedroom but my sister was not home yet.
Sometime later as I was falling asleep I heard a car pulling up outside. It was our friends dropping Anne off. I heard some voices and the car left. I dozed off and after a while I felt a light nudge. I opened my eyes and I saw my sister grinning at me. It took me a couple of seconds to realize that she only had a flimsy nightie on and that her nipples were clearly showing!!
I was speechless and then Anne whispered "Show!!"
Suddenly I was 100% alert and ready!! I whispered back "You first" and I was expecting her to say the same but then she did something unexpected: she lifted the seam of her nightie from her knees to her waist!!
I realized two things then: one, my sister wasn't wearing ANY underwear, and two, she was so horny that her cunt juices had started streaming down the inside of her thighs!!
My immediate reaction was to reach out with my hand and touch my sister's cunt. Anne let me touch her, which was quite unusual for her, to be so eager, all the while grinning like a Cheshire cat, and I could see she was biting lightly on her bottom lip.
Meanwhile, I was in utter heaven. I had dipped my fingers deep inside my sister's soaked cunt and I felt like a kid opening his best Christmas present ever!! Anne let me enjoy her womanly treasures for a few seconds and then she pulled away a little, reminding me of my end of the bargain. Then she said this was her way of saying "sorry" about my missing the beach today, even though it was not her fault in any way.
I asked her if she was willing to take her nightie off and I would take my shorts off in return so we would both be completely naked for the first time ever (something I was trying to achieve for a long time, to no avail).
She said she would love to do that, but not today (her standard reply, usually...). She said, with the way she was dressed (...), wearing at least her nightie, it wouldn't be difficult to react in the case of an emergency - meaning that if we heard our parents' door opening she could go straight to the kitchen which was the closest room and pretend she's looking for something in the fridge and no one would know she didn't have any panties on.
She promised, though, that very soon, but better during the night when it's much easier to pull it off, we would both take all our clothes off and we would do anything I wanted.
"Anything??" I asked suspiciously.
"Yes, anything" Anne said, looking straight into my eyes while she reached with her hand and slowly grabbed my rock-hard cock over my shorts.
"Let me see your big fat cock NOW, big brother" she whispered lustfully.
I really didn't know what had gotten into her and made her so horny, but one thing's for sure: I wasn't going to complain!! I complied immediately. With one swift movement I pulled my shorts down to my knees so I would also be able to react quickly myself if needed. My steel-hard prick sprang into attention feeling longer, thicker and harder than ever.
As soon my sister saw it her eyes opened wide and she made a mock gesture as if she was fainting because of its impressive size - something that she used to do to mock me, but in a nice, flirty way.
This time, though, because she was so horny, she looked a lot more serious. Her eyes were glued to my manhood as she reached, without warning and without asking first, and got hold of my meat pole.
"Wow, Marky, baby, you really are my BIG brother, aren't you??" she said, licking her lips.
I almost came, right then and there. Anne started slowly and lovingly massaging my dick with her right hand, going up and down the whole length, while massaging my swollen balls with her left. I started wondering if this was a dream: if it was, I did not want to wake up - ever!!
I know my dick is not the longest in the world (maybe 7 inches or a little more) but I know that my girth is above average - even my wife has told me that. That was the case even back then with my sister.
I felt it was my turn: I reached with my hands and slowly cupped her amazing big breasts over her nightie. Anne was cautious and felt uncomfortable with her breasts, precisely because they were quite big.