In a quaint military town in Hokkaido, Chise, a seemingly ordinary schoolgirl with a delicate frame and average intellect, cherishes her bond with Shuuji, her childhood friend and classmate. Their peaceful high school days revolve around gossip and the daily trek up 'Hell Hill.' However, their lives take a drastic turn when a tragic air raid strikes Sapporo during a shopping trip, claiming lives and igniting a brutal war. Amidst chaos, Shuuji witnesses a startling sight: Chise, now a cyborg with steel wings and a formidable armament as a result of involuntary transformation into a lethal weapon. As the conflict escalates towards their town, their relationship faces turmoil, prompting questions about Chise's humanity.