An alien space craft crashed into Graviton City, wiping out the entire population and leaving a massive crater where Graviton City is rebuilt. Students A-ko Magami and her best friend C-ko Kotobuki, a bubbly, carefree optimist, enter a new year of school at the all-girls Graviton High School. Although A-ko possesses superhuman speed and strength, she considers herself an average teenager; she mostly worries about getting to school on time, chronically oversleeping her alarm clock each morning. The pair catch the unwanted attention of B-ko Daitokuji, a rich, spoiled and brilliant fellow student.