Shuuji and Chise are third year student at a high school in Hokkaido. The shy Chise is finally confessing to Shuuji, and finally two of them are starting to exchange diary awkwardly.
One day, Shuuji tried to escape from a sudden enemy air raid on Sapporo. While desperately escaping from the air raid, Shuuji saw a scene that he could not forget for his life. He saw Chise, with a huge weapons which looks is part of her hand, shot the enemy fighters one by one. Apparently, Chise is the ultimate weapon with destructive power which is important for the war.
How can Shuuji face the reality that his love is actually the ultimate weapon with destructive power?