The 1121st platoon of the Helvetian army, stationed in the Clocktower Fortress in Seize, welcomes a new recruit in the youthful and energetic Kanata Sorami under these conditions. She joins the military to pursue her passion of learning to play the bugle, and she eagerly accepts the guidance of Sergeant Major Rio Kazumiya, who also happens to be a superb trumpeter. They are joined by the aloof mechanic Nol Kannagi, the spunky gunner Kureha Suminoya, and the sympathetic Captain Felicia Heideman; together, they discover the beauty of life in Seize and the lasting joy of a community that has persisted in the face of a disintegrating world outside them.