Hinako, a younger sister who was asked by her sickly sister to "child-making SEX" with her brother-in-law husband. Hinako, who was perplexed by her brother-in-law's obscene gaze every day, decided to accept her request for her sister's sake. However, contrary to the earnest thoughts of such sisters, her brother-in-law forgets to make her a child in Hina Koto's SEX. And Hinako gradually changes her body and mind.
