This happened when we were younger but...
Growing up in a house with my Mum and my sister (let's call her Carole) meant that I soon discovered the joy of knickers. My Mum's were fantastic, so sexy, satin, and always part of a lingerie set. I admit that I wanked off into my Mum's a few times but it was my sister's knickers that really got me going.
It all started when I realised the joy of wanking, well no, it didn't. I'd found both of their knickers so sexy for a while, especially worn ones! But when I learned how to wank I was in heaven. I would take a pair of sexy knickers and rub them over my cock as I wanked.
Eventually, and I was not that old, I asked my sister if she wanted to see. We had shown each other our intimate parts before so this seemed to me to be the next step. Carole seemed delighted too. So we were staying at my grandparents house and we were upstairs alone so I asked if she wanted to play. She said yes. I took off my clothes and laid on the big double bed upstairs. I asked if I could see her knickers and she pulled up her skirt. She had a very tight pair of pink nylon knickers on. I was instantly hard and started to wank. From the look on Carole's face she was liking what I was doing.
It didn't take long for me to cum, all over my tummy and she said it was as if my cock had 'sneezed'. When I asked if she liked it she said yes and we agreed to do it again. I asked her if she did the same sort of thing and she said she did. When I asked her to show me she said no.
The next day she asked if I wanted to sneeze again. Obviously I did. I told her it would be better if I had her knickers to sneeze into. Carole said that would be okay so we went back upstairs and this time she took them off, showing me her lovely pussy. I wanked for all of several strokes and came a massive load into her knickers. This went on for several days, each time getting more daring, she would help me with her knickers wrapped round my cock.
We have talked about our young experiences lately and both agreed it was great. She showed me the knickers she now wears and wow, they are so fucking sexy. More to follow, I hope.