Recently, the younger brother has been caught reading their father's porn magazines and trying to spy on their mother masturbating. Worried about his behavior, older sister Yuna attempts to scold him, but upon hearing the misinformation he's picked up, she ends up feeling sorry for him instead. When her brother starts asking anyone and everyone about masturbation and sex, Yuna shyly decides to take matters into her own hands. "This is a secret between just the two of us, okay?" she says, spreading her own genitals to begin giving him a real sex education.