About spring break, my older sister Harura and my younger brother Yusuke came to visit my grandfather's house in the countryside. Although they are different in age, they are good friends. One day, Yusuke witnesses Harura having an affair with an old friend of hers who she reunited with. In order to clear up the misunderstandings about her younger brother who doesn't know her, Harura decides to use her own body to give her younger brother sex education...
