My adolescent sister has gradually developed a slightly larger chest and more womanly hips. She still feels like a child, unaware of the changes in her body. She comes into my room, calling out innocently with a cheerful smile, "Onii-chan, onii-chan." Even when I touch her slightly, she shows no surprise or caution. She doesn't get angry when kissed, and when I touch her breasts, she just giggles, saying it tickles. When I grope her ass or make movements like sex, her expression slowly clouds over. I can't resist that reaction. Soon, I'm overwhelmed by the urge to touch her for real.