We lived in a two story house with only one bathroom. TV was new and it was a time of innocents. My sister and I had rooms next to each other opposite our parents bedroom. The bathroom was at the end of the hall.
Mimi is two years older than me. I remember when we were younger we took baths together. I hated it when our parents made us stop, of course I didn't know why at the time. For as long as I can remember she walked around the house in her panties and bra. I didn't give it much thought until I started to get a hard-on. I also notice my dad watched her a lot. He too would get a bulge in his pants. Mom didn't seem to mind or say anything about my sister's state of undress but I think she got the benefit of dad's hard-on later in the night. My mom didn't walk around in her underwear but left the bedroom door open when she undressed so I was use to seeing her tits, black hairy cunt and big butt. Again it didn't mean much until my dick started swelling when I watched her.
Our family seldom closed the bathroom door so I got glimpses of mom's and Mimi's titties, pussy bush and butt from time to time. As any red blooded boy would do, I tried to sneak peeks as often as possible of them getting undressed or in the bathroom. Occasionally, I would notice Sis taking a look at my cock while I was peeing. When my parents were out at night I would sneak into their room and hide because her room was across from theirs. I could watch her play with her tits and rub her pussy. Every once in awhile she would catch me and act upset or mad but never told my parents. She didn't help the situation any, she would rub her 35 C tits against me while I was studying. On one occasion, when returning from a vacation, Mimi whipped out her left boob in front of mom, dad and me to show her tan in contrast to her big alabaster tit. But that is all she did. That is until one night.
I had been out with friends drinking and I was feeling no pain. Mimi must have been 20 at the time, making me 18 (and still a virgin). I got home and had to piss so bad I burst into the bathroom. I pulled down my pants to sit because I didn't think I could stand up to pee. Sis was standing at the sink, which was right in front of the toilet. As usual she was only wearing her thin panties and her see through bra. I sat there staring at her beautiful butt showing through the thin material. Her butt crack was so inviting I couldn't resist it. In one movement I leaned forward and pulled her panties down and began kissing and licking her ass cheeks. To my surprise she didn't resist.
She wiggled her butt back bending forward so my face slide down and my tongue was now licking her long pussy lips. She rubbed her clit as I twirled my tongue in her honey hole. As she increased the rhythm of her rub I licked faster and faster. Mimi's finger flew in frenzy as she started to moan and apparently was cumming. I was afraid she would wake our parents just across the hall. She moved to the toilet and sat down removing her bra and offering me her tits. I sucked on her big hard nipples as she grabbed my cock. She said she wanted to suck me off. As I stood up she took my cock between her full tits. As my knob rose between her boobs, she kissed the head and began to lick and suck my dick. I couldn't hold back. In few minutes I shot my cum cream in her mouth and she SWALLOWED. We stood up and kissed. Mimi said this was our secret and we could do it again sometime.