Attending a prestigious high school, Saki is sent to investigate a student prostitution ring in order to bail her estranged mother out of jail.

Once there, Saki gets bullied and emotionally abused by her classmates because of her "see-through" underwear. Falling in love with a boy named Takuya, Saki is torn between love and duty.

Soon, she befriends a classmate/prostitute Asuka, who is later murdered when her double life is discovered. Joining forces with the girls from the school, Saki takes out her personal revenge on the prostitution ring run by the headmaster and a teacher named Reiko. Her weapon is a yo-yo and her battle cry is "I will never ever forgive you!"

Sent undercover to investigate a student prostitution ring, Saki is bullied and emotionally tormented by her classmates because of her see-through underwear. Falling in love with a boy named Takuya, Saki straddles the line between love and duty.

Befriending Asuka, a classmate and one of the prostitutes who is later murdered, Saki joins forces with the schoolgirls against the headmaster and one of the teachers, the prostitution ringleaders.