In the kingdom of Liberl, a man named Cassius Bright serves as one of the land's greatest Bracers, a freelance organization dedicated to keeping peace and helping those in need. When he is called off to business in the neighboring country, his daughter Estelle and his adopted son Joshua take on his work as upcoming Bracers. But when the airship he was traveling on vanishes, his children seize the task of discovering the truth behind the incident, and rescuing their father.