Regis is an incapable soldier, bad at both sword mastery and archery, who only reads books. He meets a girl at the remote region where he was transferred to. Altina, the red-haired and crimson-eyed princess who wields the supreme ruler’s sword. She was appointed to become the commander of the remote region's army despite being fourteen years old, simply for being the Emperor's illegitimate child. However, she is holding onto her big dream without being depressed in the environment she is in. “I trust you.” Regis, who was sought from her as a tactician, stands up to the obstacles together with her. The military fantasy interweaved by the bibliophagic boy and the princess with the supreme ruler’s sword.