Reward her with some attention

You move up to her again and put your hands on her body, causing her to stop bouncing and look down. You place her hand on her flat stomach and marvel at her tight curves. The warmth of her body is getting unbearable.

You push your crotch up against her hips for a moment as you let her feel your dick getting hard. She responds by getting down on her knees, pulling her tits out of her top. You grunt, unzip your pants and push your dick up against one of her tits.

It feels good to have a little pet to jerk off on. Memories of you doing the same throughout the years are getting clearer in your head as she begins guiding your dick into her cleavage.

"You're quiet today, Marky," Alice comments as she presses her breasts up around your dick. Well no shit, you think to yourself, you've never thought you'd be tit-fucking your own sister. "Just thinking about all that money you owe me," you respond and increase your pumping speed.

"I know, right? I'm such a dumb girl with money," she coos as she breathes some hot air down on your dick. "I'm much better with pearl necklaces," she smirks as you grunt and begin cumming up between her tits, splashing her cheeks and chest.