So there we were both in silence for a few seconds, me lying in the bed naked with my penis in my other hand and her panties in my other hand and my sister's gaze directly between my legs. I opened my mouth and said that I would come to see what was wrong. I got out of bed and got dressed while my sister was watching. I saw that she wasn't wearing bra under her T-shirt and her nipples were hard.
We went to my sister's room and I began investigating what was wrong. The room had only one chair, so that was where I sat. My sister leaned over next to me to watch my doings. At the same time I got the best view at her big cleavage. I couldn't focus properly while I was staring at her cleavage. A short time later my sister complained that she was too tired to stand, and sat on my lap.
Of course, I had been all this time having a boner and when my sister sat on it I began to have real difficulty with concentrating on her computer. Even when she was sitting on my lap I could still see her cleavage.
In the end, I got the job done and my sister thanked me but she didn't leave my lap. She started to shake her ass on my dick. I couldn't handle this kind of stuff for more than few seconds and I came to my pants. My sister stood up and smiled at me. She pulled down her pants and I saw that her panties that she was wearing were wet.
She took her panties off and game me those while winking her eye. She put new panties on and pulled the pants back on and said that she would go back to see her friends.
I stayed still in her room looking at her while she took her shirt off and put her bra on and shirt back on. At that point my spermy penis was already fully risen again.
Then she left and I spent the whole rest of the day wanking and sniffing her panties.