Phil winced as his cock twitched and jerked excitedly up and down. Delicately, Katy ran her fingers up his cock shaft, pinching the tip. She lifted the crown of his hard-on and stared hungrily at the even bigger-looking underside, at the pulsing vein that seamed his cock.

"Katy, don't do this to me," Phil said helplessly. "You're my kid sister!"

"I know who I am. You don't have to tell me!" Katy wrapped her little hand around the base of his cock and squeezed tightly. Immediately it started to pulse and jerk lewdly in her fist. The bloated, shiny-skinned prick knob loomed in front of her face, and a glistening drop of pre-cum appeared on the piss slit.

"Phil, do you jack off when you look at the pictures in your dirty magazines?" Katy asked innocently. "Do you jack off a lot?"

"Katy, for God's sake."

Katy squeezed his prick hard. "Answer my question or I'll tell Mom and Dad!"

"I… I do?" Phil stammered. "That's what I have them for."

"Like this?"

Giggling hornily, Katy pulled up on his cock shaft, dragging the loose flesh with her hand. She pushed her fist back down, seeming, to stretch the skin on the mushroom crown of his prick.

Phil gasped and did nothing to stop her. Katy started to beat her big brother's cockmeat, moving her fist in a blur up and down the rigid stalk of cock flesh.

"Katy, oh Christ!"

"Fuck, your cock's getting even stiffer! It's getting fatter, too!" Katy's pussy was a slick, foaming pool of lust as she gave her brother a hand-job with growing speed and expertise. "Do you like the way I jack off your cock, big brother?"

Phil only grimaced and started working his ass cheeks, fucking his prick through the tight grip of her fingers. Kath noticed that more and more hot drops of pre-cum seeped from the tip of his cock.