Hyogo Kaji serves as the commanding officer of the flying battleship Amanohara, set during the historical period of the Russo-Japanese War. In this capacity, he oversees military operations and strategic decisions, directing the vessel on its critical journey toward the battle at Port Arthur. His authority extends to supervising the specialized combat unit known as the Lime Unit, as well as managing the personnel assigned to this group. Kaji's leadership is defined by his operational control over the Amanohara, including during engagements against forces led by Grigori Rasputin.

In terms of relationships, Kaji works closely with key figures aboard the ship, including Sumi Ichijōji, who serves as the head of medical staff, and a spiritual entity named Kuki, whose power enables the vessel to fly. His role involves making tactical decisions during combat scenarios, particularly those that utilize the Lime Unit's unmanned mecha. The character's presence is consistent across the series' official media, including its television adaptation and original video animations, with his narrative focus centered exclusively on his duties aboard the Amanohara. No further information is available regarding his personal background, internal motivations, character development, or any notable abilities beyond his command and tactical responsibilities.