I'm Dan. I'm 18 and I live at home with my Mom, Dad and sister Rachel. I'd like to tell you a bit about my family (they may come up in this story).
My Mom is called Janet and she 43. She has long brown hair and an 'athletic' body. Slim, small breasts. I had seen her in a bikini plenty of times and often she would go around the house in just her underwear so I had seen enough of her to know (not that I would look...much).
My Dad is called Martin and he's 43. He has a little middle aged spread but other than that a handsome man.
Rachel is 20. Her hair is brown naturally but she bleaches it and has it cut shoulder length. She has the same slim body and small breasts as Mom. She also shared my Mom's habit of going around the house in her underwear (I did look much).
We were all sat around the breakfast table talking and Mom asked me "Is tonight your work party?"
I worked as a mail boy for a lawyers firm and we were having a staff party.
"Yes but I don't think I'm going."
"Why not? I thought you were looking forward to it."
"I was but I kind of dug myself into a hole. I was trying to impress everyone at work and told them all I had a hot girlfriend. If I turn up alone they'll know I made it all up."
"That was silly but can't you just tell them she's sick or something?"
We talked about my situation for a while. Mom was being very comforting and helpful in the way Moms usually are and Dad and Rachel were making fun of me in the way Dads and older sisters usually do. Eventually it was Mom with a kind smile and stern words about self confidence who convinced me to go.
Later that day I was ready for the party (I mean dressed for it but still not keen). I was nervous about what to tell my friends about my 'girlfriend'. Mom and Dad were sitting on the couch together when I was about to leave.
"I'm now going, wish me luck." I said to them.
"Wait! I'm coming too." I heard my sister say behind me. We all turn to see Rachel stood there looking sexy as fuck. She was wearing a red dress with a low V cut showing a lot of bare chest and clearly she wasn't wearing a bra. It was a short dress stopping only just below her ass showing pretty much all of her nylon covered legs. Her red stilettos and red lipstick both matched her dress.
"W..what do you mean you're coming?" I managed to stutter whilst drooling.
"Well it was stupid of you to lie about having a girlfriend but I'm not about to let anyone make fun of my loser little brother, that's my job. I'm going to the party with you and we'll show them your 'hot girlfriend'."
"Aah, that's sweet of you." Mom said. I was still struggling to speak (and struggling to hide that fact).
"That's because I'm the best sister. Wouldn't you agree Dan?" She asked me with a smile.
"No chance they'll believe it, she's too hot for for you." Dad joked.
"Actually, you are the best big sister. Thank you Rachel, you're a life saver."
"Tonight I'm the best 'girlfriend' ever, and you're going to owe me big for this, let's go."
As we walk out to the car I was feeling good about this plan. Nobody at the party knew any of my family, Rachel was definitely hot. This was going to work. When we got to the car I opened the passenger door for Rachel then got in to the drivers side and set off.
"I think we should clear up a few details before we get there." Rachel started "Firstly did you tell them your girlfr.. I mean 'my' name?"
"No. All I told them was that you were hot and you've got that covered."
"Good, it'll be easier if you can call me Rachel. Most brothers don't call their sisters hot though." I suddenly realized how blatant I had been and blushed. "Don't worry, I am hot." she laughed.
The rest of the journey we cover all the details like how long we'd been together, how we met. We arrived at the venue the firm had hired for the party and I parked the car but before we got out Rachel turned to me and said "There's one more thing we need to do."
"What's that?" I asked.
"We should kiss."
"Kiss? Why?"
"Well we'll need to look comfortable kissing so we should practice before we go in."
"We've kissed each other lots of times, it's no problem."
"No stupid. Not a brother sister kiss, a girlfriend boyfriend kiss."
It honestly hadn't occurred to me that in order to pretend she was my girlfriend I would actually have to pretend she was my girlfriend, kissing and all.
"Can we?" I asked "Is it OK for siblings to.."
"It's fine" she interrupted "and we're going to have to if we're going to convince people. Just relax."
We both turned in our seats a bit and leaned in for a kiss. As soon as her lips touched mine my whole body tingled electrically. It started as just a little peck on the lips but then, with Rachel taking the lead, we opened our mouths and our tongues touched. We were then having a full on passionate kiss. It was amazing. Rachel was a great kisser and the fact she was my sister seemed to make it even better. After a moment Rachel broke the kiss and we looked at each other smiling. I suddenly became very aware of my erection and hoped Rachel wouldn't notice.