Your step-sister sips something you left in the kitchen for your girlfriend, she starts to feel weird and grows bigger, it happens over and over until she is so big and powerful AND horny!! She rides on top of her step-brother's cock as she grows bigger and continues to talk about how big she is and how she will destroy things and be able to be seen for miles!! Giantess, step-sister, step-brother, growth, giant, big, huge
