My brother and I have the exact same blood type, so even if we had a child, we wouldn't know who the father would be! —Hamazaki Rio IEND-002

The eldest sister-in-law harbors sexual dissatisfaction with her brother because she took care of their mother six months ago. Meanwhile, the younger brother's husband leads a mundane sex life. One day, the younger brother has to go out, leaving Rio alone at home to care for their mother…