Me and my little sister watched the house while my parents were out celebrating.

It got late, I figured my sister went to sleep and checked on her.
But outside her door I could tell she was awake... and...

... Masturbating?

I burst in and caught her in the act. She couldn't deny it.

But I also didn't want her to stop. In fact I wanted to join her.
I took off my clothes and showed her my erect d*ck.

She seemed ashamed of what I was doing but was obviously fascinated.
She couldn't take her eyes off it. As instructed, she touched it.
Then I rushed her.

My sister gave up the fight pretty quick.
Her body was mine to enjoy until morning.
Over and over I let out all that pent up cum.

[From DLsite English]