On a winter night, I'm relaxing with my sister under the kotatsu in the living room. Even though our parents are in the next room, my mind is blown away when I see a glimpse of her panties under her miniskirt. Under the kotatsu futon, I gently run my hand up her thigh. She trembles. "N-no... Big brother..." she whispers, but every time my fingers brush her inner thigh, she lets out a hot sigh, and her panties are already soaked. My sister bites her lip, desperately trying to hold back. I show my fingers...