I've read so many stories on here about brothers and sisters. Some probably true and others not true. Mine is true!
I was fortunate enough to have a really wonderful sister growing up. We did everything together and spent a lot of time together. I remember back when we were as young as six (me) and five (her) we played 'show me yours and I'll show you mine' games. We would expose ourselves and let the other look.
We continued to play this little game until one day when I was maybe 10 I was showing mine and for some odd reason it got hard! I didn't really know why it stood up like that sometimes, but I knew it felt good. Starting then as we played that game she would tell me if she wanted to see it hard and standing up or soft.
By the time we were about 13 and 14 we each knew why it stood up! From then on she always wanted to see it up. We were each growing pubic hair by then too and that made our little game more interesting. Also, I had learned about masturbation so these little fun episodes were about to get more interesting.
By ages 14 and 15 we were each openly masturbating ourselves and each other. By ages 16 and 17 we would sneak one of Dad's porn videos from the hiding place in their bedroom closet and watch it together laying on my bed. Of course, we had to do this when we knew our parents would be gone for hours. We would lay together on the bed naked and she would rub her clit and finger herself as I jacked off watching the porn movie. I remember she loved seeing me cum.
By ages 18 and 19 sometimes we would rendezvous in one of our beds after each of us had a date and compare notes, she telling me all the hot sexual stuff that happened with her and her date and me telling her about mine, then we'd slide our pants off and masturbate ourselves or each other.
By age 21 my sister had a really serious boyfriend and we stopped playing with each other. They eventually got married. There have been times over the years when I wanted to ask my sister if she were willing to do it again but I could never get up the nerve. Those were fun days!