My sister

The door opened just after I managed to close the shower curtain far enough to be well hidden but open enough to still see most of the bathroom. Cassie, my sister, entered the bathroom and shut the door behind her.

"Man, family is annoying", she said to herself. "I need some me time desperately."

'Preach it sister', I thought and watched her walk to the toilet and sit down.

She then did something I didn't expect: Cassie flipped her skirt up and revealed that she wasn't wearing any panties, which gave me a perfect view of her clean shaven pussy. The view almost made me gasp and my dick started growing hard.
'God dammit', I thought. 'This is my sister! Stop it, cock!'
But then as my sister moved her fingers down to her pussy, controlling my dick was impossible. Cassie's fingers slowly massaged circles around her pussy lips and grabbed one of her tits through her shirt. She was practically already soaking wet and I had the best view of her, without being seen myself, since my sister was busy with pleasuring herself.
Cassie now started rubbing her clit and slowly pushed a finger inside, causing herself to moan. My own hand unconsciously moved down to my cock and I started rubbing it through my pants. Remembering I had panties in one and a dildo in the other, I moved the panties up to my face to smell them, the intoxicating pussy smell only making me more horny.
All sense was lost as my sister pushed another finger inside her pussy and pleasured herself more, which caused my horny mind to drop the dildo so I could rub my cock again without having to move the panties in my other hand. Only after already having dropped the dildo, did I realise what I just did. My eyes widened as the pleasuremaker hit the ground of the shower loudly.
I could see my sister looking up and heard her gasp, as I ducked away further behind the shower curtain.