The series centers on Yui Yūri, the daughter of a death row convict imprisoned for enacting the "greatest terrorist attack in the Heisei era." At the time, Yui was nine years old, and was judged not to have been involved in her father's activities. Now she is a second-year high school student at Takekura Kosugi High School, where the Japanese prime minister and his security detail are conducting a visit. But a paramilitary force assaults the school and takes the prime minister and the students hostage, without issuing any demands. In the middle of the crisis, Yui tries to find a way to get out.