In the dawn of the Golden Age of Aviation on planet Prester, retro‑futuristic sky vehicles known as vanships dominate the horizon. Claus Valca, a naturally gifted flyboy, and his fiery navigator Lavie are fearless racers, obsessed with becoming the first sky couriers to cross the Grand Stream in a vanship. When the high‑flying duo encounters a mysterious girl named Alvis, they are thrust into an endless battle between the rival nations of Anatoray and Disith, who are systematically destroying each other according to a code of chivalric warfare. Lives are lost and legacies determined as Claus and Lavie attempt to bring peace to their world by solving the riddle of its chaotic course.