I was in my room playing video games one night when I heard Jen, my little sister, say, “Let me know when I can show you something, big brother.”

“Sure, just give me a minute,” I muttered. I got to a good stopping point and paused my game. “What do you want?”

Jen was wearing lime green pajama pants and a black tank top that was cropped high, leaving all of her belly uncovered. She lifted her arms over her head and started bouncing up and down while saying, “Day twenty-nine, but who’s counting?”

Jen was only 14, but her display made me realize how much she had filled out recently. Her large breasts were bouncing wildly under the black tank top. It was form fitting, so her breasts were in no danger of bouncing free. The sight still had my eyes nearly popping out of my head and set my heart to racing. I was also drinking in all the bare skin around Jen’s belly button and how much her hips had flared out in contrast with her narrow waist. What she said was perhaps more important. It was late at night on the second to last day of November. I had indeed been participating in a No Nut November challenge. I hadn’t told anyone, but I wanted to see if I could go thirty days without cumming. My cock now felt like a bar of hot steel inside my jeans, throbbing and burning with pent up need. “When had little Jen turned into such an incredible babe?” I wondered to myself.

I closed my eyes, but imagining my sister’s lewd display was, if anything, worse than actually watching it. I was so horny, and she was so sexy! I could feel an orgasm building, and I tried standing up in a last ditch effort to get my cock under control. With a groan, I realized I was too late, and a wave of indescribable pleasure passed over me as, after twenty-nine days of being denied, my cock was cumming. It seemed to pulse endlessly, pumping more and more jizz out of my overstuffed prostate. Although I was irritated with my sister for spoiling my attempt at the challenge, I was also feeling absolutely unreal pleasure. Experiencing an orgasm after more than four weeks without one was a mind blowing experience. I was leaning heavily on my desk as my orgasm continued. Once my cock finally quit pumping cum, I opened my eyes and looked at my sister.

Jen was smiling at me impishly and asked, “What’s wrong, big brother? You weren’t really trying to complete a No Nut November, were you?”

I checked the clock; it was eleven PM. I had been so close! “Yes, I was, Jen. Twenty-five hours. That’s all I had left. If you had waited just a little more than a day, I could have done it.”

Rather than admitting any fault in causing me to fail my self-imposed challenge, Jen asked, “What’s that white stuff on your jeans? Did you cum so hard that spunk soaked all the way through them already?”

“I don’t know, probably,” I admitted. “I had nearly a month worth of jizz stored up.” I unsnapped my jeans and unzipped the fly, revealing soaked boxers and even more hot, sticky cum. It was much nastier and thicker than I was used to, which had to have been a result of how long some of that jizz had been inside me.

“What kind of pervert are you that you’re unzipping your pants to show your little sister how you creamed yourself?”

“It’s your fault!” I snapped. “Why did you even think I was trying for No Nut November, or that bouncing around in front of me would derail me?”

“I wasn’t sure, but I had noticed that there weren’t any cum stains on your sheets when I was doing laundry the last few weeks,” Jen explained.

My mind was reeling. My little sister had noticed cum stains on my sheets? Before Jen took over the laundry, had our mother noticed? Jen noticing was humiliating, but I wasn’t sure if it was more or less embarrassing if Mother had noticed or not. Then something else occurred to me.

“You little brat! You’ve got curves now, and you wanted to test them out on me! What was your logic? That if you could make your brother cum, you must really have a sexy body?”

“I didn’t think putting on a little show for my big brother would make you ejaculate; I was just trying to see if you would notice I had those curves you’re talking about! I guess I got my answer,” Jen protested.

“Well, you did make me cum, and now I have to wait a whole year if I want to try to complete this challenge!” I snapped. I advanced on Jen to confront her face to face. She kept sidestepping, and we kind of circled each other in my bedroom. “What kind of pervert are you that you think getting your own brother to notice your big tits or sexy figure is a good idea?”

“What kind of pervert are you that your sister’s bouncing boobs made you cum so easily or that you can’t stop talking about my curves and sexy figure?” Jen asked back.

“I’m not a pervert; I just hadn’t nutted in almost thirty days. Almost any bouncing boobs could have set me off.” While I was awfully horny with just over a day to go in the challenge, I admitted to myself that Jen’s tits were incredible. That had a lot to do with why I hadn’t been able to get my cock back under control. Between those big boobs bouncing and her incredible hourglass figure, my little sister had certainly become very sexy. I don’t know what came over me; maybe I really was the pervert. I fished my still hard cock out of my boxers to show Jen. “Look at what you did, Jen! I’m still hard, and there’s even more cum inside my boxers than what soaked through!”

“That is a whole lot of nut!” Jen admitted before changing her tune. “What are you doing, big brother? I’m only fourteen; put that thing away!”

Now that I had cum once, I realized that my body wanted to cum again. Despite the size of my orgasm, I still felt uncomfortably full of jizz, and the recent memory of how good it felt to pump that jizz through my hard cock had me aching to experience that feeling again. Then something else finally occurred to me. There had been a clapping noise when Jen was bouncing for me, but she hadn’t been clapping her hands. It had to have been her ass cheeks slapping together from the way she was moving. I spun Jen around to get a look at her backside. Words were flying out of my mouth so fast I hardly knew what I was going to say: “Damn, Jen, you have some serious junk in your trunk. That ass is thicker than a bowl of oatmeal! Is that what was responsible for the clapping noise I heard?”

“Yeah, I was wondering if I could get you to notice that too,” Jen admitted. “But you don’t have to be so crude about it.”

Jen turned to face me again, and she was between me and my bed. I pushed on her shoulders, causing her to step backwards and sit down on my bed. I pushed again, causing her to lose her balance. She fell flat on her back, and her legs flew up. I stepped between them and tugged on her pajama pants. They came down to mid-thigh, revealing that Jen hadn’t been wearing any underwear. “Who’s the bigger pervert now? Me or the bratty girl who tried to give her older brother a boner without any panties on?”

“I can’t make my ass clap with panties on,” Jen explained as if that should have been perfectly obvious to me. “Now, what are you doing, big brother? Let me up; I won’t do it again.”

“Just a second,” I told her. I started rubbing the head of my cock on Jen’s bare pussy lips. There was so much cum on my cock, I was smearing thick white spunk on the outside of Jen’s pussy.

“What are you doing?” Jen demanded again with more urgency. “Don’t you know how dangerous that is? You could get me pregnant, big brother, just from the cum already on your cock!” Jen’s pussy was causing a sensation so intense, it almost felt like the tip of my cock was on fire. Somewhere inside my brain, I knew my sister’s words made sense. However, I also knew that there was relief to be had if I could get those pussy lips to spread apart for me. All the cum on my cock must have acted like lube, because slowly but surely, my dick was sinking into Jen’s body. The way her snatch put pressure on my cock was amazing; every little bit of contact and friction only made me crave more. I had to get deeper into my little sister’s pussy!