My sister, Harper, is fifteen years old, about five feet two inches tall, has a mass of wavy honey-blonde hair that cascades halfway down her back, an astonishingly cute face with the biggest cornflower-blue eyes, full and soft-looking heart-shaped lips, perfect little perky B-cup breasts (often unencumbered by a bra), a firm but beautifully rounded little butt, and slender legs that look fabulous when she wears one of her short skirts or pairs of lo rise shorts.

I suppose, as her older brother, by roughly a year, I shouldn’t be describing my sister in some of those terms, or have the longings and yearnings for her that I do, but I can’t help it - she’s just so gorgeous and sexy. That would be bad enough, but Harper very much takes after our mother. Mom is about three inches taller, her boobs are a D-cup (yes, I did look at her bras in the laundry to check), and she’s more curvaceous than Harper, with an ass that Kim Kardashian herself might be envious of, but other than that, they could be mistaken for sisters.

Am I ashamed that I fantasise about them? Yes, I suppose I am. Does that make me stop imagining them naked, or how their gorgeous tits would feel in my hands? No, it doesn’t. Or the cheeks of their awesome butts? Or what it would feel like to kiss their lips? Or see those lips tight around my knob? No, not even a little bit.

Although my mother doesn’t generally display quite as much flesh as Harper, her clothes always seem to cling to her, much as I’d dearly love to, emphasising rather than hiding her luscious curves.

Both of them cause my pulse to quicken and my underwear to become uncomfortably constricting, but it’s Harper’s school uniform that regularly sends me limping to my room. Her blouses appear to be at least one size too small, straining to contain her breasts, which themselves are only really enhanced by the half-cup bras tantalisingly visible through them. And her skirts, so short that it’s a constant wonder to me that her panties aren’t permanently on show, rather than just the occasional heart-stopping glimpse. Just imagining my mother dressed in Harper’s school uniform is enough to make my cock so hard that I worry it might burst.

I’m sure that most normal teen boys masturbate pretty frequently, but, as you might imagine, with Harper and Mom around, I’m horny almost constantly, and have to retire to the privacy of my room on a very regular basis.

I do have access to porn, but, as often as not, as I near my climax, I have my eyes shut, dreaming of Harper ... or Mom ... or both! Yes, that’s right, I regularly fantasise about them naked together ... hugging ... kissing ... licking.

I’m always very careful about locking my door so I’m not disturbed, and using headphones so that I can listen to the dialogue and the lovely noises that the girls make without anyone else hearing. And, before you ask, yes, I do have quite a collection of mother / daughter videos, both lesbian and hetero, and yes, quite a lot of them are blondes.

I normally jerk off as soon as I get home from school, and then ... let’s just say, multiple times after I go up to bed.

I was in full swing to one of my favourite vids of a lovely mother who decides to teach her son and daughter about sex by having them practice on each other, when, out of the corner of my eye, I saw my door opening. My pulse rate shot through the roof as I realised that I’d forgotten to lock it. Harper’s face appeared in the gap, and her eyes opened wide as she saw what I was doing. With one hand, I tried to cover my junk, and with the other, I pulled my headphones out. “ ... so sorry,” was all I heard of what she’d said.

I waited for the cries of ‘Ew!’ or ‘Pervert!’ or whatever, but she just opened the door wider and stepped into the room, squinting between my legs as if she wanted to see more of what was hidden behind my hand.

The thought that she might have liked the glimpse she’d seen made my erection, which had started to flag a little, perk right up. I decided to go for it and took my hand away. I saw a small smile play over her lips as she pushed the door closed with her butt.

“Maybe you’d better lock it, if you’re staying,” I suggested as I wrapped my hand around my dick and slowly stroked it up and down. Without taking her eyes from me, she reached to her side and turned the key in the lock.

I couldn’t believe it! My innocent little sister actually wanted to watch me jerk off!

She was wearing the uniform that I described earlier, and looking at her gorgeous boobs and long, slim legs was thrilling enough, but it was the look of lust on her face and the way she kept licking her lips as she watched me that had me hard as an iron bar with a drop of precum leaking out of the tip.

“You can come closer, if you’d like?” I suggested. Without saying a word, she shuffled over until she was standing next to my bed.

“I’ve never seen a real one,” she whispered, almost to herself. I’d never had the opportunity to stare at her legs so closely before, and I was fascinated when she began to rock gently from foot to foot.

“Do you like it?” I asked, cupping and caressing my balls with the other hand as I continued to stroke myself up and down, caressing the ridge below my knob.

She pondered over my question for several seconds. “I love the shiny tip,” she said finally, “and the way it somehow looks hard and soft at the same time.”

She stood there, nibbling on her lips and swaying, while I got more and more excited. At times, I thought I got a whiff of a scent so delicious that it made my head spin, and I wondered if I was smelling a girl’s sexual excitement for the very first time. The idea that Harper was getting turned on by what I was doing made my hand move faster.

“Are you going to cum soon?” she asked.

“Maybe,” I admitted. In truth, I could have cum anytime in the last five minutes, but I didn’t want what we were doing to end. All sorts of crazy ideas went through my head, but I didn’t want to risk anything that might upset her. I decided to take a small chance. “Maybe, if you showed me the front of your panties...?” I suggested, and then held my breath.

“Really?” she asked, sounding surprised.

“Uh-huh.”

Her hand seemed to move in slow motion as she took the hem of her skirt between her thumb and forefinger and then lifted it. My hand was a blur as the tiny triangle of whiteness slowly got larger. It lovingly hugged the shape of her pussy, the faintest shadow hinting at where her slit was. But it was the tiny darker patch at the bottom that had my hips lurching as the first spurt blasted onto my chest; Harper was wet! Her pussy was wet!!

“Oh,” she said, her eyes following the second jet from my cock to my belly. “Oh, my. There’s so much,” she said, and giggled as it kept on coming. I’d never cum so hard or so much in all my life, and my eyes kept going from her sweet pussy to the rapt and delighted expression on her face, driving a few last shuddering spurts from me.

She carried on watching me as I used the handily-placed box of tissues to clean myself up, apparently so caught up that she didn’t think to lower her skirt.

“Do you do that often?” she asked when I was clean and soft.

“Well, quite often,” I replied, too embarrassed to tell her the truth, which was utterly insane, bearing in mind that she was currently looking at my cock.

“Can I watch you do it again?”

“I do it pretty much every day before Mom gets home,” I told her, “and yeah, I’d love for you to watch me.” Mom had her own boutique in town, and she always got home a good hour after us, so I knew we’d be safe.

The very next day, Harper caught up with me as I was walking home. She looked around very guiltily to see that no one was watching us, which I found adorable, before asking in a whisper, “Are you going to ... you know ... do it?”

My cock started to swell immediately. “Yes, I am,” I told her, and her gorgeous blue eyes sparkled with excitement, and she smiled happily as she skipped along next to me.

We went into my room, and she locked the door behind us as I took all my clothes off. Just having her eyes on me meant that I was fully erect before I even lay down on the bed.

“Do you want to see my panties again?” she asked, her face turning bright red.

“Do you think...?” I began, and then faltered. What if it was going too far? “Could you ... do you think you could take your skirt off? Please?” I don’t think I’d ever been so happy as I was when she gave me a tiny, coy smile.

“‘kay,” she whispered, and then undid the fastening and took her skirt off. This time, she had on pale pink cotton panties, and I nearly came on the spot as she turned around to look for somewhere to put her skirt; they’d ridden up between her perfect cheeks, leaving half of them bare.

When she turned back to find me jerking off furiously, she giggled, turning back again and then looking over her shoulder at me, “Do you like my butt?”

“Oh, Harper,” I moaned, “it’s beautiful. Could you pull your panties a bit higher? So I can see a bit more?

She gave me the naughtiest little smile and then slid her fingers along the edge of each leg hole, settling her panties into the crease between her gorgeous cheeks. They were utterly perfect: beautifully curved, and the unblemished skin was so close that I could see the fine, downy hairs covering it.

I cupped my balls and stroked my cock as I tried to commit every last detail to memory. How would it feel to nestle my face between them and feel their silkiness against my own cheeks, I wondered, and instantly my hips were bucking, and I was covering my chest and belly in rope after rope of cum.

Harper just giggled and watched wide-eyed, twerking her butt a little to help me along.

“I love watching you do that,” she said softly.

“I could do it again. In a few minutes,” I suggested hopefully.

“That’s enough for one day,” she said fondly, and then she amazed me by bending over and giving me a little peck on the lips. “You’ll have to think about what you want me to do tomorrow,” she said before she picked up her skirt and let herself out.

What do you want me to do tomorrow? The words rang in my head. She wanted to do more!!

I don’t think I learned a thing at school the next day. I desperately wanted to see her pussy, and half the time, I convinced myself that she might do it. Then I’d flip the other way and tell myself that boobs would be great. Boobs or pussy? That was the question that occupied my mind pretty much all day - boobs or pussy?