Kevin was on the home stretch of a particularly long jacking session when his sister opened his door and entered his room. He was sitting at his computer desk with his browser open to one his favorite porn sites, currently playing a video on loop of two hot women engaged in lesbian sex. Both were blonde, with one of them completely shaved and the other sporting a cute trimmed bush above her glistening pussy lips. The first blonde with the bare pussy was going to town on her counterpart, munching and sucking on the other's pussy hungrily. Kevin would have busted his nut at this part if not for the interruption.
"Hey Kev," his sister, Brooke, said nonchalantly and completely unfazed by what he was up to. "You seen my iPad?"
Kevin didn't take his eyes off the screen but he shook his head while continuing to pump his lotion-covered cock. "Nah, sorry. Check the basement."
Brooke, wearing jogging shorts and a tank top, watched the screen along with him for a moment. She was standing in silence, not seeming disgusted in the slightest but actually intrigued.
"Damn," she said after a few moments, "they make it look so hot, don't they?"
Kevin was pushed over the edge by her comment, and helped along by her presence since he enjoyed masturbating with a female audience, and groaned as he shot off in front of her. He kept his dick pointed straight up and squirted cum onto his belly and thighs. He had been building up his load for almost a half hour already, being his first wank of the day, and had noticed that jerking off for longer the first time made it easier to cum again later. He sighed raggedly as his sister watched him jerk the last few drops from his cock before letting it go finally. It lurched once as she watched him enjoy himself.
"Feel good?" she said with a smile.
He nodded and smiled. "Oh yeah. Thanks for letting me finish."
"No problem." Brooke seemed genuinely happy to oblige him. "Can you go check your car please, after you get cleaned up?"
"Yeah sure." He grabbed a towel from the floor next to him and wiped the cum from his body. Then he threw on some shorts and a t-shirt before fetching his keys.
He had just turned eighteen and Brooke was a year older but still lived at home while she took her gap year before starting college. They had an older sister as well, Madison, that had moved out but was frequently seen hanging out at the house still. Their family was fairly close, more so than most that they knew, so it was welcome. The three of them got along great, and most of that was due to their mother's strict family rule regarding their behavior around each other growing up.
She was fairly liberal, and a self-proclaimed hippy during the day, but Muriel Weathers was known around the community as the happiest widow in town. Of course being a widow was not cause for celebration, but she had promised to raise her three children on her own in a warm and accepting household that would fill the void of a father with unconditional love. Her own upbringing had influenced her joyous marriage before her husband passed away from illness, and though her children had been young at the time and didn't remember much about his death, thankfully, she had come out of the experience determined to be "that mother" who nourished her children's curiosities and never made them feel anything but positive things.
One thing, among many, that she was completely open about with them was sexuality. She made no attempt to hide her own sexual needs from them, and proudly established the bedroom as a personal space that no one was allowed to bring negativity into. If you wanted to do something in your own private space and others were allowed into that space, then that meant they had to accept whatever you were doing regardless of what that was, within reason of course. She also wasn't a fan of locked doors, ironically, as that was a person excluding themselves from the rest of the family. It was a balance of respecting someone's privacy without invading it, while simultaneously being allowed into that private space as proof of love and acceptance.
Muriel believed that allowing children to act unfettered gave them the freedom to learn for themselves, which would make them into self-actuating members of the community. Her one strict rule for the family was to never make someone feel bad for what they did. That was the only rule and it had to be followed exclusively or else she would find creative punishments that usually involved the offender doing nice things for the one they offended. Fortunately for her, the children had grown up respecting each other as she had wanted. Their family life, while missing a father, was still full and rich and loving.
One thing that had not happened as of yet, though it was not really spoken against, was sexual interaction between them. Muriel hadn't enforced any rules about that because it hadn't seemed necessary up until now. The children had viewed sex as something to never be ashamed of, so there was no need to sneak around in secret attempting to have sex or explore each other's bodies. Sex was an open book in their house so if they wanted to fuck someone they certainly had opportunity, but they were also fairly attractive people and didn't have any issues finding partners in the wild.
Both girls had lost their virginities years ago, and Kevin had within the last year. Muriel was proud that they were being safe and open about it. No curbing of appetites was necessary, and she actually found the thought of them being sexually active a bit alluring. Incest was one of her own kinks but she was so diligent about being a good parent that she would never even mention that around them. They had had discussions about fetishes and kinks over the years and knew that it was a deeply personal thing not to be brought up without the information being offered first.
Later, Kevin was hanging out in the living room on his own device, scrolling through memes and sexy images in the various subreddits he belonged to, when Madison came through the front door.
"Hey bro," she said, throwing her purse on the floor and heading for the kitchen.
Kevin barely registered her, but something about her outfit caught his attention just as she disappeared around the corner. She was wearing a bikini top and denim shorts, showing off lots of skin. He had to admit that he liked seeing his sisters scantily clad, and even better seeing them naked when the opportunities presented themselves. Since he was raised to never be embarrassed about such things, he found that he quite enjoyed being naked around them too. His cock wasn't huge or anything but he was proud of it nonetheless.
Madison returned with a soda in hand and plopped down on the couch across from him. "Bro."
Kevin looked up from his phone. "Yeah?"
Madison leaned forward as if she was about to share a secret. This made her cleavage, ample and full, take his full attention. "Wanna play around tonight?"
Kevin smiled. "Sure. You horny?"
Madison nodded. "Hell yeah. Actually, FUCK yeah."
Kevin snickered. She knew that he got off on hearing women swear, and also that their mother wasn't fond of cursing in the house. However, she would never stop them from doing it.
Kevin looked back to his phone but his attention was diverted now. "What about Brooke?"
Madison was casually stroking her inner thigh at the moment while sipping from the soda can. "I think she's actually gonna go fuck Sean or something. I can't remember but she seemed excited to go out."
Kevin was getting aroused again, and in his shorts it was plainly evident. He made no attempt to hide it from her.
"Nice," she said, eyeing his boner. "God, I kinda wanna do it right now."
Kevin was ignoring his phone now, upon hearing that. "I thought you said we were gonna go swimming at the rec when you go home. You want to jerk off before, or after?"
Madison thought about it while openly rubbing her mound through her denim shorts.
