A defenseless, busty sister gets fucked by her super-strong younger brother. She thought she was seducing her virgin brother, but... it turns out to be a surprise!

Yuzuru, who had enrolled in a prestigious boarding school famous for table tennis and lived a life of club activities that were unable to immunize women, had returned to her parents' home for the first time in a while. Meanwhile, Yuzuru's sister Ai also fights with a married couple and returns to her parents' house. Ai, who was stressed out during a conversation, learns that Yuzuru is still a virgin, and seduces her as a joke, but in the midst of puberty, she takes this seriously, and the innocent younger brother, who sucks on her sister's huge breasts... and eventually cums inside her...