My sister was and still is an attractive girl. She had a slim body and great boobs that were perfect. When I was 13 years old, I found out that you could see into my sisters room through the top or the old air vent in her ceiling from the attic. A couple of years before that, we had some kind of air conditioning replacement, so they created a new vent in the ceiling and moved all the pipes to that one. So what was left was a vent that did not work. It was always closed, but sometimes if I wanted to spy on her, I would go open it.
I could also only do this on the rare occasion that both of my parents were gone and my sister was home. When she would get into the shower, I would sneak in her room and open the air vent and wait for her to return. I saw her naked most times I tried this. She would wrap herself around with a towel while waling down the hall, and then get into her clothes while she was in her room. But something new and unexpected happened one day.
It was a day that both my parents were gone, and I can't remember why. My sister was 16 at the time, and I was 14. It was later in the evening, and my sister was about to take a shower. I thought that this would be a good opportunity to see her, so I went into her room, opened the vent a little bit so that she would not notice that it was open, and climbed into the attic. I closed the latter so she would not know that I was up there. I crawled over to the broken vent, and looked inside. I was waiting there for a good while.
Finally, I heard her turn the water off, and I knew that she would be in here at any minute. I also made it look like I was asleep by turning my lights off. She walked into her room, and dropped her towel. I was amazed. And sometime between the time before that I saw her and the current time, she had shaved her pubic hair, which made me even more horny. Then she put on a pair of panties and a bra, and left the room. I was disappointed because I thought she was done but then I heard her asking if I was asleep at my door. And of course, I did not reply and she came back to her room. Then she did something that I did not expect at all.
I saw her take her bra and panties back off, and lay on her bed. The moment she did this I was really excited because I knew what she was about to do. She started to masturbate! At this point I was very horny and had a massive boner. She was fingering herself and moving her hips in a certain way that made it look even more attractive. She was fingering herself with the left hand, and rubbing her boobs with the other.
She kept doing this for a while then all of the sudden she lifts up her hips, takes really deep breaths, moves her fingers really fast, and lets out a couple of soft moans. I was amazed, and as she stood up, I could tell that there was a small wet spot on her bed cover. I was rock hard and could not wait to get back to my room.
I watched her wipe and put her clothes back on, and then she laid on her bed and went to sleep. So I quietly climbed out of the attic and into my room. I pulled down my pants and started wanking as hard and as fast as I could. That was the best orgasm I ever had and probably the most cum I have ever made.
In future, I was able to see her only a few times because again, my parents were rarely away from home at the same time.