Since moving to Tokyo, I've returned home every summer and winter. With my parents gone, my sister's family now lives in my childhood home. My sister Risa is cheerful and curious, while her daughter Lala is innocent and pure. I've always taken care of them, but over time, my nieces gradually grew from children into young girls. Though their bodies matured, their minds remained childlike, and they would cling to me each year saying, "Onii-chan, let's play," leaving me constantly flustered. Last summer, when I came home, Risa suggested we play doctor as usual. Touching her delicate frame and developing chest aroused me, and before I realized it, I had made her suck my cock and came inside her small mouth.