Disambiguation: This article refers to the location. For the episode of the same name, see Grand Stream (episode).
The Grand Stream is a location of significant importance in the Last Exile anime.
The Grand Stream is an air current, a continually rushing 120-knot (140 mph) storm that circles the center of the hourglass-shaped planet of Prester. The torrential storm always rages in the high altitudes of the skies of both Anatoray and Disith and is thought to be all but impassible – even giant capital ships must follow paths of relatively calm air current. If even a skilled pilot attempts to go into the torrents he has a great risk of getting lost, crashing, or being destroyed by the large hulking form of Exile. Disith has managed to map these currents by following the migratory path of rainbirds. Throughout the series, most believe attempting the crossing in a Vanship to be tantamount to suicide.
The Grand Stream cannot be seen from the ground of either Anatoray or Disith; looking up, one sees only clear blue skies. It seems there is some form of barrier that hides the Grand Stream from view. The Silvana can be seen exiting from the Grand Stream and entering the blue skies of Anatoray at the beginning of the episode First Move. There are quite a few people in the series who tried to cross the Grand Stream. Hamilcar Valca, Georges Head, Alexander Row and Euris Bassianus were the first ones who attempted to cross the Grand Stream with Vanships. But in the end because of the Exile and Maestro Delphine Eraclea's interception, Hamilcar, George and Euris died at the expedition. Alex somehow managed out of that chaos alive. Later, Claus Valca, Lavie Head and Alvis E. Hamilton crossed the Grand Stream successfully together.
The first attempt to cross the Grand Stream in a vanship was made by Hamilcar Valca, Georges Head, Alex Row, and Euris Bassianus, who were trying to deliver the Anatoray-Disith Peace Treaty. However, the crossing failed due to the interference of Maestro Delphine Eraclea, resulting in the death of all but Alex Row and a long conflict between Anatoray and Disith.
Alex left his specially-modified vanship, Spirit of Grand Stream, to Hamilcar and Georges' children, Claus Valca and Lavie Head. Claus and Lavie vowed to one day succeed where their fathers had failed and cross the Grand Stream together.
Claus and Lavie achieved their dream in the episode Resign. Shortly afterwards, Alvis E. Hamilton activated Exile, abolishing the Grand Stream. The barrier that hid it from view also disappeared, allowing one to see Anatoray in the sky of Disith and vice versa.