The lone battleship Silvana locates a Disith fleet crossing the Grand Stream and destroys several ships in a surprise attack. After the remaining Disith ships escape, the Silvana withdraws from the Grand Stream. In the frontier town of Norkia, fifteen-year-old pilot Claus Valca and navigator Lavie Head prepare their vanship for the Norkia Cup race. On their next job call as sky couriers, Claus and Lavie accept a mission to deliver two letters to Duke David Mad-thane from his family. David, an officer in the Anatoray navy, is leading a battle against a Disith fleet at Minagith under the supervision of the Guild. After a victory in the opening engagement using musketeers, the Mad-thane fleet continues to battle the Disith in artillery combat. However, the Mad-thane fleet meets a surprise attack from a new Disith fleet as Claus and Lavie arrive on the flagship Claimh Solais to deliver the letters.