Unskilled in both swords and bows, Regis is a soldier who ranks last in military academy and is obsessed with books. After being banished to the borders, he met a girl who changed his destiny. With her red hair and crimson eyes, Princess Altina possess the sword of kings. Daughter of a royal consort, she was appointed as the commander of the border regiment at the tender age of 14. But she did not lament her circumstances and bears higher aspiration. "I believe in you." Regis accepted the request of the girl to be her strategist and forge through many hardships. The sword princess and the bibliophile youth embark on their fantasy war story.