Me and my stepsister—she's clearly into me, extremely shy, and has an unbelievably cute smile. Somehow, we've started dating. We haven't had sex yet, but now we have a rare overnight chance while our parents are away. I decided to seize the moment, making out and fooling around nonstop. At first, she barely let me touch her, but as we kept going, she gradually changed. In the end, she transformed completely, begging me, "Cum inside me, big brother," turning into an insatiable nymphomaniac.