During spring break, my sister Harura and my younger brother Yusuke came to visit my grandfather's house in the country. Although he is a year away, he is a close brother and sister. One day, Harura is witnessed by Yusuke about an affair with an old friend who reunited. In order to resolve the misunderstanding of his younger brother who has no knowledge, Haru decides to give sex education to his younger brother with his own body.