So, my sister and I have always been really close. We've always shared a room, and even shared a bed for a while when we were younger.

So we became a lot closer than regular sisters, we'd always get changed together, see each other naked, even shower together. It was never a big deal.

We'd sometimes even show off for each other, compare underwear or our bodies.

One thing that you quickly realise when sharing a room with someone, is there's no private time. We both had quite high sex drives and would want to masturbate regularly.

Initially, we had an agreement to only do it while the other was out, or if we walked in on each other to not make a big deal of it. Eventually that turned into doing it while we thought the other was asleep, which inevitably lead to us both doing it quietly in our beds at night.

We didn't really acknowledge it, just had some sort of private agreement. This went up until one night, we were both masturbating and aware the other was doing it too, and she let our a fairly loud and obvious moan. She told me later it wasn't on purpose, but it didn't stop me from moaning back. Me copying her kinda of broke the ice, because we both more openly moaned and made noise until we both finished.

We both slightly acknowledged each other and giggled. We didn't really say anything but knew we unlocked something new... because from that point on we'd more openly masturbate at thr same time.

As we got more comfortable with it, we'd start to do it openly on our beds, look over at each other. Eventually made the jump of doing it side by side, watching porn together.

We didn't do anything sexual together for a while, but it wasn't long before we did acknowledge it. We made jokes about what it'd be like to do it, teased each other about going down on each other or what we'd do to each other if we wearnt sisters. To be honest, it got to thr point we were touching ourself to our dirty talk rather than the porn.

I could tell we were on the edge of touching each other for months, just waiting for the other to make the first move. And that happened one night, we were home alone so both fully naked, very loud with our moans. We were laying side by side and she put her leg over my thigh, I was desperate to touch her and knew it was an invitation, so I almost immediately slide my hand down her tummy, waited for a nod from her and started fingering her hard. Wasn't long before she returned the favour, and after we both finished all we could do was giggle.

After that, we went to eat together, then went back to bed a couple hours later. Within a few mins of us turning thr lights off, she asked to join me in my bed, and we had one of the best nights of sex ever.

Since then, it's become a pretty regular thing, almost daily when we can. We don't tell anyone, and know it's just a casual thing so won't be upset if we wanna be with other people.

Over time our sex has become incredibly intimate and loving, as well as dirty and kinky, and tbh I don't wanna stop any time soon.

Thank you sm for reading :) happy to do a part 2 or more details if you'd like