Incest Seduction/Tell Kim where her hand is
"Kim?"
"Mhmm?"
You try to think of a way to say it more delicately, but after a moment you just have to blurt it out.
"Your hand is on my dick."
She giggles, shifting her hand back and forth.
"No it's not!"
What? That's not the reaction you were expecting.
"Umm... yes?"
"No. It can't be!"
She rubs up and down the top of your dick a few times, much too fast and deliberate for any kind of 'honest mistake'. The sudden stimulation makes your cock quickly swell and lengthen.
"Kim, seriously, you're tota-"
You're shocked into silence as your sister grips onto your cock through your sweat pants. She squeezes and rubs it more vigorously while acting as clueless as ever.
"Really? THIS is your penis?!" Kim adds another slow tight stroke through your sweats, punctuating her words. "I thought it was your leg!"
You're beyond words now, amazed that your little sister would not just touch your dick, but literally pump it to life. You may have wanted to sound authoritative or even violated but it's hard to come off that way considering that you continued to pet your sister throughout the entire encounter.
"Silly me! Sorry about that!" She slowly pulls her hand down and off your member. "I don't know if this makes it any better, but I'd be willing to let you go tit for tat.... if you wanted."
She groped you thoroughly. It's only fair that she receives the same treatment.