My sister is a super high school girl who can't stand it

Manami, a high school girl, is threatened with lewd photos taken by a teacher trainee and continues to have perverted sex. On the other hand, her brother-in-law searches through Manami's room, watches her masturbate, and indulges in masturbation. Manami confides her worries to her email friend, who she doesn't know is her brother-in-law. To the brother-in-law who saved his beloved sister...the best ending!!