Your stepsister needs cum for her science experiment. A lot of cum...
Sexy, but it needs work. She keeps swallowing the samples, and she's treating this more like a scientific discovery, more than a project done for a grade. Maybe a subplot where the project is an excuse to seduce the stepbrother? And maybe make the science more "playful curiousity", and less "serious discovery."
She keeps saying she's looking into my eyes, when she's sucking my cock through a glory hole. She talks to me when we're in separate rooms. She swallows my cum when she's supposed to be saving it in a specimen jar. smh...she needs better Scenario instructions.