Julia F. Reinhart serves as the Captain of the Spica Platoon within the Space Defense Force, the organization responsible for protecting the galaxy's railway lines. Her career began after graduation when she signed up for the SDF and was initially assigned to the Acrux Platoon. It was her notable analytical ability and high intelligence that led to her promotion to the Captain of the Spica Platoon.

In terms of personality, Julia is described as bright, yet she possesses a stubborn and inflexible side when it comes to her duties. Despite this rigidity, she is deeply caring and carries a strong sense of responsibility. These qualities foster a deep trust among her crew members, who tend to view her not just as a commanding officer but as an older sister figure.

Her professional role in the story often brings her into conflict with Ryusaku Murase, the Captain of the Vega Platoon. Their friction stems from Julia's reluctance to relinquish command, which clashes directly with Murase's tendency to act before thinking. Julia demonstrates notable abilities in strategy and analysis, which are the hallmarks of her leadership style and the foundation of her command. Her character development revolves around navigating her high sense of duty and her interactions with other strong-willed officers, balancing her inflexible nature with the caring instincts that define her as a leader.