I live in a very open family. We talk about everything, and we joke around with each other and tease each other. It's a lot of fun, with me and my sister, Jen, and my parents. For a brother and sister, we get along pretty well. When we were younger we took baths together, up until we were about ten. But even then, we were never really embarrassed to see each other naked. We would walk out of our rooms to the shower and back without covering up, and it was no big deal. Even our parents would sometimes walk around naked, or my mom would be wearing only panties while she made breakfast.
When I turned fifteen or so, I began to experience sexual feelings whenever I saw my sister or my mother naked. It was usually never enough to give me an erection, though sometimes it did. I couldn't help myself, and after a while my mom began to notice that I was uncomfortable whenever she or my sister was naked. It wasn't like they would walk around naked all the time, but if it was hot then they would go topless, and while they were getting ready, they would be mostly naked.
So one day my mom told me that I shouldn't be embarrassed if I got an erection. She gave me the "it's only natural" speech, but I was still embarrassed. However, the next time I had an erection when my sister came by naked, I know she saw it and yet she didn't seem put off by it. She acted as if it was completely normal, and maybe she even expected it. Neither my mother nor my sister relented in their nudity.
My dad was naked a lot too, mostly after he came home from work and showered. We ate a lot of dinners in the nude, and after a while it felt great, and I wasn't nervous about getting an erection around my family. In fact, one time my sister sat playfully on dad's knee just for a moment, and he started to get hard. Both my sister and my mom teased him about it, and he laughed with them.
Things were great at my house, and the summer when I was eighteen they became unbelievably better. My sister was one year older than me, and my parents were both in their early forties. By this time I was glad erections were accepted in my family, because my sister had developed a smoking body. Usually the thing that got me every time was her glorious ass. Occasionally, when we were alone, I would brush up behind her so I could grind into her ass. I don't think it was really sexual for her, but she always smiled and gave me a sensual remark jokingly.
Of course, by this time I was a frequent masturbator. This wasn't always easy, since my mom and sister would always walk into a room without knocking. A few times I would be laying on me bed jacking off, and my mom would come in with some laundry, or my sister would come in to borrow something. Being nude, there was no way to cover up. But they didn't seem to mind, they would see me with my dick in hand and act as though I was simply preoccupied. "Oops, just let me set this here" or "Let me just grab this and I'll be out of here". They knew I was whacking it, but they accepted it as normal.
It was when I started walking in on Jen masturbating that things changed. I opened her door and walked into her room to see her fingering herself on the bed. She closed her legs around her hand, her other hand fondling her breast. She had a nice medium rack. Considering she and my mother almost never wore bras, they had great tits, firm and pert.
"Oh, sorry," I said, just standing there.
She smiled, not seeming embarrassed. "That's okay."
I went to retrieve a CD she had borrowed, and saw that she was waiting for me to leave.
"Don't stop on my account," I said.
After a few seconds, while I took my time finding the CD, she began to fondle her breast again. Then when I turned, she had resumed fingering herself, but not as actively. I stood there watching her for a moment, and I was beginning to get hard.
"Look at you," she teased. "Am I turning you on?"
"Sorry," I said, a little embarrassed.
Jen opened her legs very sensually, licking her lips, and slowly massaged her mound. She was such a tease.
"You think you're the only one who gets off when you're alone?" she said. "I know when you're jacking off in your room, or in the bathroom."
I laughed nervously. "How often do you do it?"
She shrugged, propping herself up on her elbows. Her breasts were pushed out, giving my a pleasing view of her cleavage.
"A couple times a week," she said casually. "Why?"
"No reason, just curious. Has mom ever seen you?"
"Sure, she knows I do it. She knows we both do it. It's normal."
I sat on the edge of her bed. I was used to the sight of her naked body, and quite a sight it was. But now it was different, we were both aroused. I was still hard, and I could smell the scent from her sex. Her arousal wasn't fading.
"If it's normal," I said smoothly, "then why are we doing it in private?"
She smiled, knowing where I was going with this. She cocked her head.
"What are you saying?" she asked, playing along.
"Maybe we could help each other out."
Just then she ran her hand up and down my chest. I let out a moan.
"What if mom sees us?" Jen asked. "What do you think she'll do?"
I knew my mom pretty well, and we were a very open family to the point of intimate. But this was beyond that, this was purely sexual. I loved my sister very much, but this was not a romantic encounter. I could see the lust in her eyes. She wanted it as much as I wanted it.
I began to stroke my dick, and she resumed rubbing her pussy. I felt like I was going to cum very soon, so I relaxed and enjoyed the sight of Jen getting off. Her eyes were glued on my rock hard penis as she frigged herself. Her free hand played with her tits, pulling at her nipples. When she started to tense up, I couldn't help but resume stroking myself.
She groaned and threw her head back, and I knew she had cum. She whined and bucked her hips, and her breathing was erratic while she climaxed. By the time she finished, it was all I could do to keep from squirting my load. She breathed deeply and looked down at me.
"You didn't cum?" she asked in surprise. She scooted closer to me and put her hand on my thigh. "Cum on my stomach."
She put her legs on either side of me and pulled me to her until our groins almost touched. My balls were slapping her cunt as I jerked off. When she touched my chest, I couldn't take it any more. I grunted and released my semen onto her. Jen smiled in delight as my cum roped over her flat stomach. When I was finished, I had left five very powerful jets of sperm all over her. She touched it and rubbed it around.
"I've never seen it this close before," she said.
I sat back and sighed, taking in the sight of her naked body with my cum all over it. She smiled as her eyes met mine.
"That was fun," she said, tugging at my dick. "What next?"
"How about dinner?" came a voice from the doorway.
Our heads whipped around to see mom standing in the doorway, wearing only a pair of panties. She smiled as she saw our guilty expressions.
"Come on, you two. Your father is waiting."
