Hibiki lives with her younger brother and father. Being a caring sister, she is always attentive to her father's actions, who is an avid AV enthusiast. One day, her brother accidentally stumbles upon her father's porn collection and becomes shocked by the content, developing a distorted understanding of sex. Distraught, he breaks down and confides in Hibiki. Determined to provide proper sex education, Hibiki decides to use her own body to gently and thoroughly teach him the truth about real sex. A story of deepening family bonds and supporting her brother's emotional growth.