As the summer stretched into fall, no more erotic incidents happened between my step sister and I, but she was all I could think about. I wasn't even interested in other girls in my town, that were closer to my age. I was suddenly taking notice of the developing curves on her body, the self-assured way she walked around. Lia was no longer the gangly, stick-thin sister, that I ignored. She was emerging into a sexually charged teeny bopper, or so I imagined in my head.

My planned confession to her, about what I saw on that basement sofa, faded away. I just couldn't bring myself to start a conversation about it. I suspected that she knew I saw her naked pussy on display, but pushing this further demanded a courage that I didn't have at the time. That, and the fear of being caught by our parents, or my big brother, and living with this family shame, was enough to keep me muzzled. 

I was taking a shower after soccer practice one day when I heard the bathroom door open, and then some muffled giggles. I recognized my sister's voice, but couldn't make out the identity of the other one. The shower curtain was being slowly inched open on one side, and I heard more soft giggles. To my amazement, I didn't try to yell at them or cover my dick with my hands. I had a nice dark tan from the long summer of sports, a fairly muscular frame, and I was not ashamed of the flaccid size of my cock. Quite the opposite, in fact. When I had an erection, I admired the curve and protruding veins along the shaft. The base was thicker and just tapered slightly down towards the head. My cock quickly shot up to attention, when I could sense that there were eyes on me. I pretended that I didn't know they were peering at me from the side of the tub, or even care, for that matter.

The power I felt as I displayed myself to these girls was intoxicating. It gave me the hardest erection I've ever had. With both eyes closed, I arched my back as I rubbed shampoo through my hair, swiveling my pelvis more towards the voices, so my hard cock seemed mere inches from their faces. I snuck a peek at them, as I was rinsing my hair under the showerhead. The second girl was our next-door neighbor Cheryl, who was about the same age as Lia. They were both kneeling down and level with my crotch, near the far corner of the shower curtain, and both had locked onto my hard twitching cock with their wide eyes. 

Suddenly Cheryl shouted, "Flag pole! Flag pole!" and quickly shut the curtain. I heard her scampering out of the bathroom, laughing. I then sensed the curtain slowly being pulled back away from the wall. Though water was running into my eyes, I caught sight of Lia staring straight at my cock. I continued my act of pretending that I didn't know she was there, and started running a bar of soap down over my chest and then onto my cock, working a thin lather up and down the shaft. I slowed down the stroking motions because I was incredibly close to that point of no return; into the throes of orgasm. This was like a lucid erotic dream, and my heart was pounding. I kept my eyes shut, and pictured my sister with hungry eyes, looking with wonder, up and down my wet tanned body, and finally resting on my throbbing dick. 

I was so close to exploding from my light stroking, that I decided I was going to let her see me cum. I couldn't hold back anyway. I made sure to use my right hand, so she could see the entire length of it, as I brought myself over the edge and exploded. There was a desperate whimper as I lightened my grip and stroked heavy gobs of cum onto the wall of the shower. My dick is only average length, but in that few moments, with Lia watching this intimate act, I felt huge. 

The last spasms were tailing off when I opened my eyes and saw a delicate brown hand sliding the curtain back over to the wall. The bathroom door creaked open, closed again, and I was alone. I stood quietly straining to hear the little voices on the other side of the door. I barely made out the voice of Cheryl saying, "He did what?....that's so gross! You watched your own brother beat his meat?"

Lia replied in a hushed voice, "It was amazing...and hot...and he's not my REAL brother you jerk!"