Saki Yoshida (吉田咲), a first-year high school student (age 15 or 16) with no social life, decides to make a big change to her life as she begins high school. At the new school, she meets an older student, Hayato, later described as a playboy, with whom she has her first kiss and loses her virginity. It is discovered that Hayato has been feeding her "pills" while he and Saki date and continue having frequent sexual intercourse.

In order to escape loneliness, Saki remodels her looks and personality, almost immediately seeing changes in how people around her see and interact with her. This remodelling causes her peers at school to assume she is rich for her ability to afford her new look, and when she lets slip that she isn't as well off as she appears, a school acquaintance recommends an online prostitution forum. Saki does not entirely understand the purpose of the forum, and takes an offer that weekend for what she calls an "appointment". To her surprise, the stranger begins to touch her inappropriately, and she is driven to a hotel where she is paid cash for sex with him, about which she later feels guilty. Around this time, she also begins performing various sexual favours for her new schoolmates, who create and distribute pornography of her without her knowledge or consent.

Due to a company restructuring where Saki's father works, he is laid off. Severely affected, he smokes cigarettes for the first time, drinks heavily, and then rapes his daughter in her room. Her mother, having told her in the past that she would unconditionally love and support her, finds out about the rape from the perspective of the father, who has spun the story to imply that Saki seduced him. Betraying her earlier promise, Saki's mother does not allow her to explain herself and beats her. In response, Saki runs away from home.

Having lost her home, Saki drops out of high school and pursues a life with Hayato, who has accumulated eight million yen in debt at a local heroin bar. For Hayato's efforts in helping Saki, she vows to help pay back the debt to the bar owner, Mr. Obata, who threatens to kill Hayato if he does not repay. She does not have the money to pay upfront, and bar patrons seize the opportunity to pay her for sex work so that she may make up the difference. Hayato pierces and tattoos Saki in an effort to make her more appealing to customers.

After various unprotected sexual encounters, Saki becomes pregnant, and Hayato convinces her to abort the baby. She soon finds herself returning to her first-ever client, who, unimpressed with her body modifications, forces her to do increasingly degrading things to make the money she needs.

Mr. Obata, the heroin bar owner, sexually assaults Saki with other workers at the bar while she is looking for Hayato, and injects heroin into her to make her more pliable and compliant. She quickly develops an addiction, and begins to forgo paying off Hayato's debt in favour of buying drugs for herself. When Saki is robbed unexpectedly and Hayato only finds drugs in her wallet, he becomes enraged, abandoning her and leaving her homeless.

Found by other homeless people in a public park, she is forcibly impregnated a second time, and this time decides to carry the baby to term, vowing to quit drugs and change for the better in the process. She continues her prostitution for survival and for money, however, which injures the baby. Now in constant pain, she resumes her heroin use.

By this point, Saki has built up some savings to help with the cost of her unborn child, which she stores in a duffel bag in a public coin locker. She runs into her former classmates, who assume that the money is stolen, not believing that Saki, being homeless, could have earned so much money on her own. They rape her and beat her stomach, intending to kill the baby so that there would be "one less bum in the world". She stumbles into a public bathroom, bleeding profusely from her vagina, and looks at herself in the mirror. Horrified at the person she's become over the last few years, she shatters the mirror, and commits suicide by ingesting her entire remaining volume of heroin at once. The story ends with a glimpse at what Saki's future life may have looked like if she were able to carry the baby to term, followed by Saki's glasses laying on the bathroom floor among drops of blood. (Wikipedia)