This happened when I was 17 and my sister, Jasmine, had just turned 16. It was the beginning of the school year, probably late August or early September. I was a senior, Jasmine was a junior. Our parents are divorced and we live with our mom. She was working a third shift job at the time this happened, but since I had my license, it wasn't a problem because I would drive myself and Jasmine to school every morning. Since mom was never home in the mornings, Jasmine and I had the house to ourselves. This usually worked out perfectly because I would get ready in the main upstairs bathroom and Jasmine would use the smaller bathroom that was connected to our mom's bedroom since mom was still at work while we were getting ready for school.
When this happened, the plumbing in mom's bathroom was screwed up and would leak down into our kitchen, so Jasmine and I had to both get ready in the main bathroom. This was really a pain for both of us because we both took a long time in the mornings. The first week, we were late to school three times because we took to long getting ready. Jasmine and I were never super close. We got along alright and were friendly enough with each other, but that was all so we never shared the bathroom when getting ready.
I usually masturbated at night, but one morning I was feeling extra horny so I decided to rub one out before I hopped into the shower. I was fully hard and jacking away when I heard noises coming from the hallway. I paused and listened more closely. I couldn't make out what the noises were and curiosity got the best of me and I opened the door to see what was going on. Imagine my surprise when I opened the bathroom door to find Jasmine, stark naked, leaning on the wall next to the bathroom door, masturbating.
I gasped when I saw her and covered my hard dick as best as I could. Jasmine stopped immediately and started to yell at me.
'What the fuck?!' She screamed.
'You were the one finger fucking yourself in the hallway...' I told her.
'Fuck you!' She screamed, getting up and running back into her room.
I felt bad. I hadn't meant to find her, or make her embarrassed. It was then that I realized that she was listening to me jacking off while she was fingering herself. I wrapped my towel around my waist as best as I could with my dick still semi-hard and walked to her door. I knocked.
'GO AWAY!' She yelled.
'I'm coming in.' I warned.
'What?' She snapped, as I opened the door.
'I'm sorry. I wanted to apologize.' I told her.
She just looked at me.
'I didn't realize what you were doing. I opened the door because I heard noises and I didn't know what was going on. If I knew what you were doing, I wouldn't have opened the door.' I said.
'Thanks...' She mumbled, still not really looking at me.
'Hey, it's okay.' I told her.
'It's embarrassing.' She said.
'It was kinda hot...' I said. Maybe I shouldn't have gone there.
'Really?' She asked, making eye contact with me for the first time that morning.
'Yeah, really.' I confessed.
We just looked at each other.
'Would you like to come in and we can finish what we started?' She asked.
'Uhm, YES!' I replied.
I dropped my towel and sat down on her bed. She took off her bathrobe and threw it on the floor. Without saying another word we sat on opposite ends of her bed, facing each other, and masturbating. I was so horny, I knew I wouldn't last too long. Within a few minutes I felt my orgasm building and building and it hit. I squirted rope after rope of cum, unintentionally, all over Jasmine. This must have sent her over the edge because she began convulsing and shaking and let out a low moan followed by a massive sigh. We just lay there panting and looking at each other's naked bodies.
We showered together that morning and went for round two. The rest of the school year we both got ready in the master bathroom together, occasionally masturbating together but mostly just being comfortable being naked around one another. That day definitely made our relationship stronger and brought us close together. While we did occasionally masturbate together after this, it didn't become a regular thing like some people talk about. I am now away at college and Jasmine is finishing her senior year of high school. I am thankful for our experience and am glad that we are much closer now. And of course, on occasion, we still have some fun together.