Schweltleite is a warrior servant of the Old Gods.
During the War of the Three Gods, she was tasked with protecting Vingolv Castle and the magical golden apples contained within; following the pantheon's defeat, she and the castle were both sealed away deep beneath the earth. The angel Ilzave was appointed as her warden.
As the ages passed, Schweltleite plotted to break free, which would require vast reserves of power. Her chance finally came when Abeloos Casserly, lured by the prospect of immortality granted by the golden apples, found his way to the valkyrie's prison. At her bidding, Abeloos kidnapped Princess Latina of Rewinia as a human sacrifice. Ilzave intervened, and the sacrifice failed. However, by using the princess' body as an anchor, Schweltleite was able to project herself to the surface and gradually drain power from human townspeople.
This activity eventually catches Rewinia's notice, and when Battle Goddess begins, Celica, General Levia, and the White Dragon Knights are dispatched to investigate; meanwhile, Latina's betrothed Lorrain also comes to investigate with his own private forces. The ensuing conflict results in enough bloodshed to greatly empower Schweltleite; when Celica eventually defeats Ilzave and sets foot within the castle itself, the valkyrie is able to possess Latina's body and mortally wound him, breaking the seal at last.
The remnants of Latina's soul rebel at this point, giving the Godslayer enough time to flee; by the time he recovers, Vingolv has erupted from its prison and risen into the skies, ready for Schweltleite to seek vengeance upon humanity and the new pantheon. Celica travels to the castle a second time and engages Schweltleite in combat, eventually defeating her. She asks him to finish her off, revealing the true reason for her plot: not revenge, but to die the warrior's death she was denied. Celica refuses, telling her that her mission to protect the castle still stands; if he was able to find an Old God ages after the war ended, there must be others alive out there somewhere, and one day they will return. Accepting this, the valkyrie returns to her slumber, but not before exacting a promise: if that day does not come, then Celica will come for her in their place.