My eighteen year old twin sister, Julie, was easily the hottest girl in school. Everyone I knew I agreed on that fact. It kind sucked for me because it meant the sexiest girl around was completely off limits to me. I couldn't even count how many times I'd fantasized about her perfect body. I knew those thoughts were wrong, but I couldn't help them. It wasn't my fault she had the ability to give a guy a boner just by wearing a bikini.
Our mom and dad both had jobs that kept them away from home so much that I sometimes forgot we even had parents. That left Julie and I basically living on our own most of the time. Being left to take care of each other probably made us closer than most siblings.
The first time I ever saw my sister naked was a complete accident. I was sitting in my room minding my own business when Julie opened the door and walked in. She had a towel wrapped around her and her hair was wet. She had obviously just taken a shower.
"Whoops," Julie said when she saw me. "Sorry, Justin. I can't believe I accidentally went to your room instead of mine. I meant to go get changed."
"That's okay," I said.
I tried to play it cool, but the truth was that seeing her dressed in just a towel was kind of exciting. She was very athletic from her time as the head cheerleader, as well being captain of the school volleyball, basketball, soccer, baseball, swimming, lacrosse, football, and track teams. Her legs were perfectly toned, and her towel left them mostly bare. I wished I could have seen her butt too, since I knew how good that look when she wore tight shorts for her sporting events.
Before Julie could turn around, her towel slipped and fell to the floor. My mouth dropped open and I nearly had a heart attack as my sister was left completely naked in front of me. Her flawless round breasts and perfectly shaven pussy were on display for me. I knew I should look away, but I couldn't.
"Oh no!" Julie exclaimed, raising a hand to her mouth in shock. "I can't believe my towel just fell off while I'm standing right in front of my own brother."
She looked down at her naked body, too shocked to try and cover up. I had gotten instantly hard from looking at her, and my cock was straining in my pants to get out. I hoped she wouldn't notice my full ten-inch erection pointing straight at her.
Julie finally tried to cover herself with her hands. She put one hand in front of her pussy, and an arm across her breasts. She seemed so embarrassed to have me staring at her. I couldn't blame her, it must have been awful for her to have her own brother leering at her while she was so exposed. I still couldn't seem to look away.
She eventually decided to try and put her towel back on. She had to turn around and bend over to pick it up, but when she did I was given an unobstructed view of her perfect butt. When she bent over at the waist I could see both her little asshole and pussy both peeking out at me, I nearly died right there.
I was unable to resist any longer. I whipped out my twelve-inch cock and began furiously masturbating. Julie saw what I was doing and stood back up without grabbing her towel. She looked even more shocked than before.
"I'm sorry," I said. "I can't help it. I know you're my sister but you're just too sexy."
Julie didn't seem to know what to say at first. It took me a moment to realize that her eyes had latched firmly onto my cock as I stroked it. Instead of the disgust I expected, she actually had an expression of lust taking over her face.
"You're so big," she said with a degree of awe. "How come I never knew that?"
I shrugged. "I don't know. It's not something a sister is supposed to know about her brother."
"Well a brother isn't supposed to jerk off to his sister either," she pointed out.
Instead of respond to that, I simply let out a long groan as I reached orgasm. My fourteen-inch cock twitched and pulsed and shot an incredibly powerful blast of cum straight at Julie. I'd never cum so hard in my life, and even though she was several feet away from me, my semen landed directly on her tits. That was how turned on she'd made me.
Shot after shot of cum landed on my sister's boobs, covering them entirely in a sticky white mess. Finally my balls were empty and my cock began to shrink back down. I felt guilty for what I'd just done, and I was sure Julie was going to be pissed about it. Strangely, that didn't seem to be the case.
"Guess I must really turn you on, huh?" she said thoughtfully.
"Yeah," I said. "You're the hottest girl I know. I know I'm not supposed to think about you that way, but I do. I'm sorry."
"Hm, well I s'pose it's not the worst thing in the world. I mean, it's kind of like a compliment, right?"
"Um..."
"After all, if I could make my own brother do this," she said, gesturing to the cum that covered her chest, "that's kind of good for my confidence."
Julie winked at me and stuck a finger into the mess on her breasts. She moved the finger to her mouth and sucked on it experimentally. She seemed to like the taste and smiled as she pulled her finger back out, now clean. She bit her lip as she took a last look at my shrinking erection, then turned around. She picked up her towel and walked out into the hallway totally naked.
****
Julie spent the rest of the day teasing me. She put on her shortest skirt and her tightest top, and nothing else. She found every opportunity imaginable to bend over and show me that she wasn't wearing any panties. My sixteen-inch cock stayed hard almost constantly, which quickly became excruciating for me.
"Julie, you have to stop showing off like that," I finally told her.
"Why, what's wrong?" she asked. "I thought you liked seeing my pussy."
She flipped the front of her skirt up and made the sexiest pout I'd ever seen on her face. My cock nearly burst out of my pants at the sight.
"I do," I said. "But you're my sister. I shouldn't be getting turned on by you."
"I won't tell anyone. I kinda like knowing how horny I can make you. I know that's wrong 'cause you're my brother, but I can't help it."
"If you keep flashing me like that, I'm going to have to masturbate again. I can't help it either."
"Mmm, I can tell."
Julie stared at the enormous bulge my full, eighteen-inch erection was making in my pants. She bit her lip and absently rubbed her pussy, showing how turned on she was getting too. I was about ten seconds away from blowing my load right there.
"Maybe I should go," I said.
"No, don't go. Let me help. I'm the one who caused your problem, right? Let me fix it."
I couldn't move as my sister slid her skirt down her legs and stepped out of it. She stood bottomless in front of me for a second and just let me look. Her pussy juices were already starting to run down her thighs. I couldn't believe she was that turned on by the situation.
Julie took a step toward me so she was right in front of me, then knelt down. She undid the front of my pants and freed my cock. It was completely stiff, and when she pulled my pants down it sprang out and slapped her in the face.
