In a long-ago war, humankind set off a devastating ecological disaster. Thriving indistrial societies disappeared. The earth is slowly submerging beneath the expanding Sea of Corruption, an enormous toxic forest that creates mutant insects and releases a miasma of poisonous spores into the air.At the periphery of the sea, tiny kingdoms are scattered on tiny parcels of land. Here lies the Valley of the Wind, a kingdom of barely 500 citizens; a nation given fragile protection from the decaying sea's poisons by the ocean breezes; and home to Nausicaä.

A monk warns Nausicaä that omens of an apocalypse, Daikaisho, will appear soon and the forest will boil over to cover the land. His predictions appear to be coming true when she arrives in the Forest in the South and discovers Lord Miralupa has developed mutant spores for biological warfare, but the mold begins growing uncontrollably and there's no antidote.