Masamune, a third-year middle school student, lives in a town where all the exits have been sealed off due to a sudden explosion at a steel mill, causing time to stand still. Residents are forbidden from making any changes and spend their suffocating days in the hopes of returning to normalcy someday. One day, Masamune's mysterious classmate Mutsumi guides him to the fifth furnace of the steel mill, where they encoun...