This was the time when on the earth were Barral Kingdom, Rigüler Empire, and in the center, the wealthy country, Larcuss Kingdom. The protagonist, Diehärte Kraus, left the home of his parents to train as a knight and serve the house of Marquis William, castle lord of the floating fortress which levitates in the sky above Larcussia, the kingdom's capitol. On that day, the Northern Rigüler Empire suddenly invaded Larcuss Kingdom. In stark contrast, it was also the day of Diehärte's ceremony of ascension to knighthood. What in the world will happen next.....