My name is John, and aside from having an IQ of 172, I lead a pretty normal life. I have a sister Carrie who is three years older, hot as hell and has been the subject of my fantasies for many, many years. She's got a great body and is physiotherapist in training.
In high school I excelled scholastically while she was the more popular one, changing boyfriends every couple of months. She was gorgeous, but bitter and always angry for some reason. I guess it had something to do with the fact that mom and dad had always attended to my needs first. It wasn't fair towards her, but it wasn't my fault. Although we were brother and sister, we rarely spoke at all and usually just avoided one another. She always seemed pissed at the world and could be mean and cruel for no reason.
Mom and dad had remodeled the basement for my special projects and it was where I would go whenever I wanted to try something, build something or take something apart. It was in that basement that I discovered an invisibility serum seven months ago. After testing it on some of my pet mice and developing a counteragent, I began using it myself. It worked like a charm and I could render myself invisible at will. The only practical catch was that I had to be naked for the serum to work, as my clothes were, off course, unaffected.
It didn't take long before I realized the possibilities of the combination: being naked and invisible. I began spying on my sister and jacking off while watching her take a shower or undress. The more time I spent watching her, the more it became clear that my sister had a strange fetish; whenever no one was around - or at least she thought no one was around - she would get into these risky, erotic situations by taking her clothes off or playing with herself at inappropriate times.
For instance, one of her favorite things was to go upstairs after dinner, take off her clothes and go into my parent's bedroom to diddle her clit. Sometimes she'd call it quits after a few minutes, sometimes she'd bring herself to a climax right there on the floor, or on the bed. Once or twice, I've even seen her bring her boyfriend along and fuck the shit out of him. She would also fuck him in her own room, with the door wide open.
This one time, about two weeks ago when dad was out and I was supposed to be down in the basement, she convinced her boyfriend to take an even greater risk. While mom was reading a magazine in the dining room, Carrie snuck down butt naked, with her boyfriend in tow in nothing but his boxers. In the kitchen, about five meters from where mom was sitting my sister got on her knees, sucked on his cock for like six solid minutes and took a massive blast to her face. Although she had the whole first floor at her disposal, she had chosen that specific location, simply for the risk of getting caught.
Needless to say, I really began obsessing over her. I had been lusting after her for a long time, but once I knew what a perverted freak she was, I wanted her even more. I started spending even more time spying on her, neglecting my other projects. All of my free time was now devoted to following my gorgeous sister around to see what other stunts she would pull.
Last weekend I followed her into her boyfriend's apartment, just a few blocks away from our house. I had expected to see her fuck his brain's out, but she didn't. Aside from a quick, clinical hand job when she arrived, she turned down all of his advances for the rest of the evening. She would let him grope and squeeze her but she wouldn't put out anymore. As a result, he had a massive boner for a big part of the evening.
When it was time to go, she insisted on walking home alone, although he'd proposed to accompany her. She gave him a long, wet, sloppy kiss and then left him hanging as she headed home. I followed her, walking just a few meters behind her. Suddenly, after walking for only forty seconds or so, she stopped and reached for the zipper of her skirt. After unzipping it, she hooked her thumbs behind the waistband and pulled her skirt down, along with her panties. As she stepped out of both items of clothing, I grabbed my hard dick and began jacking off. I gawked at my sister as she turned in place and faced every possible direction for a few seconds.
She unzipped her coat halfway down, pulled it down her shoulders and pulled her arms out, unbuttoned her blouse about halfway down, exposing her light blue bra, which she then pulled up, exposing her big, but firm tits without unclasping it. After tugging her hard nipples a few times, she picked up her skirt and panties and continued walking home, considerably slower than before. I couldn't believe what a fucking slut my sister was. Her boyfriend was probably whacking off, trying to get rid of the blue balls she'd given him, and here she was, with her tits and cunt on display for anyone lucky enough to pass by to see.
Considering the late hour, it was a calculated risk and for a while I thought she'd get away with her slutty performance, until I suddenly noticed a man in his early fifties walking his dog. He had turned the corner and was heading straight for us. As soon as he noticed her, he slowed down and looked around, confused.
"Are you okay miss?" he asked, stopping just before crossing her.
Carrie didn't stop and just said, "I'm fine, asshole!"
The guy looked at her gorgeous ass, bewildered, not knowing what to do. The risk she was taking, my god, this guy could have raped her right then and there, but she just walked on, her back towards him, not a care in the world. Luckily, we didn't run into anyone else and soon arrived home. I slithered in along with her and followed her into the living room, where she grabbed the remote of the TV and flicked it on and cranked up the volume to a pretty loud level. Then, she got onto the dining room table - dressed as she was - on her knees and began fingering herself, with just the light from the TV to illuminate the room.
It was as if she wanted to get caught; mom was a pretty solid sleeper, but dad was bound to wake up from all the noise. Still with one hand tugging her nipples and the other plunging three fingers up her soaking wet twat, she didn't seem to care. It was too much for me; I just sank to my knees in the middle of the living room, right in front of her and shot my big load on the carpet. As soon as my cum left my cock, it was visible again, so I left a pretty decent stain.
Before I could figure out how to clean it up, I heard dad coming down the stairs. I moved out of the way and watched, wondering what Carrie was going to do. Although she could probably hear dad coming down just like I did, she didn't react immediately and continued fingering herself for a few more seconds, clearly getting off on the impending danger. Then, suddenly, she jumped off the table and ran into the adjacent kitchen, barely a full second before dad barged into the living room, turning on the light in both the living room and the dining room. I moved to the far wall and watched as he grabbed the remote and switched off the TV. He then took a good look around both rooms, stepping in my sperm as he passed by - luckily he was wearing slippers.
"Damn TV," he grunted as he flicked off the lights and headed back upstairs.
Carrie came out of hiding and flicked on the dining room light again, got on her knees and fingered herself to a wonderful finish, three meters away from me. She bucked and trashed, convulsed and moaned as quietly as she could. I waited for her to leave and head up to her room, then made my way to the basement where I made myself visible again and turned in for the night.
Carrie had apparently scratched her itch because she didn't do anything sexually or depraved for two whole days.
Then, on the third night, after dinner, I went to the basement, made myself invisible and headed up the stairs to find my sister. True enough, I found her clothes scattered across the night hall, including her panties and bra, which told me that no matter where she was, she was stark naked. I found her in our parent's bedroom, with just the small night light on mom's side of the bed switched on. Carrie was on her knees playing with herself with mom's pillow stuffed between her legs.
Surely she wouldn't, I thought to myself. I could smell her twat from where I was standing. If she actually came on the bed, especially on the pillow, mom was bound to notice. But she didn't care and just fingered herself, spraying her scent all over the place. Rock hard and aching for a good release, I waited for her to climax before I chose to shoot my load onto the sheets, on dad's side. You know, to even things out a little bit, lol.
That's when things went south. Instead of lying down and relaxing for a few minutes as she usually did after any kind of climax, she hopped off the bed, not on her side, but flung herself towards my side. As a result, I couldn't avoid a collision and she bumped into me, toppling over onto me on the floor next to the bed.
"Auw, shit," I said out of reflex, realizing my cover was blown.
"John?" my sister shrieked as she jumped up and flicked on the light and looked for me.
As she couldn't see me, she began getting nervous and began to panic.
"Carrie, I'm invisible..." I whispered, trying to calm her down as I crawled away from her.
"Yeah, I figured that out by myself, but how... and what the hell were you doing here?"
