The film is based on the bestselling book Gakunen Biri no Gyaru ga 1 nen de Hensachi o 40 Agete Keio Daigaku ni Geneki Gokaku Shita Hanashi (学年ビリのギャルが1年で偏差値を40上げて慶應大学に現役合格した話) by Nobutaka Tsubota.

Eventually, she attends a private all-girls high school where she plays and enjoys her extra-scholarly activities while skipping study altogether - here, she is caught and suspended for carrying cigarettes.

Her father (who aims to get her younger brother Ryuta into pro baseball despite the latter's reluctance) labels her as an "air-head" and says she and her mother are being scammed by the cram school.

Over the course of the summer holidays of her second year, through to the exams at the end of her third year in high school, Sayaka works diligently, going without sleep to the extent that she nods off in her classes, forgoing dates with her friends, and dying her hair back to black and cutting it, to show her resolve.

Her results progressively improve on practice tests and her academic deviation value increases tremendously from 30 to 70 in this short period.