Emma Rodman is a girl who strives to be a knight. She is from an interstellar nation called the Algrand Empire. She lives on the planet Hydra, ruled by Count Banfield. As a child, she saw a knight who was driving a mobile knight, a humanoid weapon. Seeing it she aspired to become a knight herself. However, in her first battle, she failed. Emma is given a “D rank” rating, making her a failure of a knight, and is shipped off to a frontier security force.