Sarana had been entrusted by her strict father to educate her younger brother Akira, but Akira's strange behavior constantly angered their father, placing immense stress on Sarana. One day, while bathing together, she found herself focusing on Akira's body and was ultimately drawn to his cock. Torn by impure feelings toward her own brother, Sarana decides to use the pretext of education—entrusted to her by their father—to teach Akira about sex. As a new relationship begins to form, she must confront her own emotions and the consequences of her responsibilities.