In a small Japanese town, a schoolgirl named Maki Taichi endures relentless torment from her classmates, who cruelly call her names because of her heavy build. Determined to escape the bullying, Maki throws herself into a rigorous diet and succeeds in shedding the weight. But her body does not stop changing. The pounds continue to fall away uncontrollably, leaving her emaciated, skin stretched thin over a protruding skeleton. Her former tormentors now taunt her with a new label: Bone Girl.

The physical deterioration accelerates into something far more grotesque. One day at home, Maki is overcome by an unbearable itching. When she digs her nails into her own skin, the flesh peels away in strips, her fingernails tear off, and the underlying tissue sloughs off to reveal clean white bone. She is reduced to little more than a walking skeleton, a literal embodiment of the nickname she was given. This transformation unleashes a horrifying shift in Maki herself. No longer a victim, she sets out on a chilling rampage, turning the cruelty she suffered back onto those who mocked her. What begins as a story of bullying and body image spirals into a nightmarish revenge tale, where the boundary between the human and the monstrous dissolves.