She does

Your sister stops for a minute. Taps you on the shoulder.

“Oh god what now? I’m not changing it.” You blurt out.

“It’s not that...” she replies blushing and avoiding eye contact.

“Okay, what then? Your arm tired? Need me to stroke it for you?” You jokingly say.

As you say that her cock twitches and precum dribbles out. This causes her to shiver, and her breasts sway seductively. Her head is downcast and her hands are under her thighs as she replies, “Um... would... would you stroke me?please?”

You stare dumbstruck by the question and totally taken aback.

You did not expect this at all, and don’t know what to think as your mind races around the issue. What’s not helping is the moaning, and fucking from the porn.

Finally, you reply “hardy fucking har. Ya damn comedian. Can we just get back to the video now that you’ve had your laugh?”

You turn your attention back to the video, but before you can start stroking again you feel someone else’s hand on your cock.

Looking down you see her small hand gripping your cock gently and follow it back to her face which is looking at you confidently, and she says, “I’m not joking.”