Warrior/pacifist Princess Nausicaä desperately struggles to prevent two warring nations from destroying themselves and their dying planet.

One thousand years after the "Seven Days of Fire", an apocalyptic war which destroyed civilization and Earth's ecosystem, scattered settlements exist throughout the Toxic jungle (Sea of Decay in subtitles and the manga translation), a forest swarming with giant insects. Everything in the Toxic Jungle is lethal to humans.

Nausicaä (Sumi Shimamoto), a princess of the Valley of the Wind, is a skillful fighter but also humane and peace-loving. She communicates with the giant insects (particularly the Ohmu: gigantic, armored, caterpillar insects who are the most intelligent in the Jungle). Master Yupa (Goro Naya), a wise wandering warrior, is dedicated to finding the legendary "man in blue" who has the power to reunite people and nature. Nausicaä is inspired by Yupa, and she explores the Toxic Jungle to help her understand it. She travels long distances by "windriding": flying an advanced jet assisted glider.

A struggle among several kingdoms ensues when an airship crashes near the Valley. Nausicaä tries to rescue a wounded girl, who reveals herself as Princess Lastelle (Miina Tominaga) of Pejite. The airship, from the militaristic kingdom of Tolmekia, carries an embryo of a Giant Warrior, one of the lethal creatures used in ancient war. The dying Lastelle tells Nausicaä to destroy the embryo.

The Pejite discovered the embryo, but the more powerful Tolmekia stole it and took Lastelle as a hostage. The Tolmekians' airship was attacked by insects, causing them to crash. Tolmekians, under the leadership of princess Kushana (Yoshiko Sakakibara) and her general, Kurotowa (Iemasa Kayumi), invade the Valley to secure the Warrior embryo. Kushana explains that the Giant Warrior will burn the Toxic Jungle, even though legends warn against this.

Kushana attempts to return to Pejite, along with Nausicaä and several new hostages. Before leaving, Nausicaä reveals to Yupa a hidden garden of jungle plants, which are not toxic because the plants grow in sand and water obtained from a deep, untainted well. Nausicaä explains that the jungle is toxic due to the fact that the soil has been tainted by man, even in the Valley. Since she has to depart, however, she shuts off the water which was keeping the plants alive.

Several Tolmekian airships are attacked and destroyed by a Pejite gunship. Nausicaä, Mito (Ichiro Nagai) and Kushana escape to a surviving gunship. They crash land in the jungle and Nausicaä communicates with several Ohmus, thereby discovering the pilot of the downed Pejite gunship is still alive. With the help of her glider, Nausicaä rescues the pilot, Asbel (Yoji Matsuda) of Pejite, the twin brother of Lastelle. However, Nausicaä and Asbel are swallowed by quicksand and end up in a strange, non-toxic world below the jungle. Nausicaä realizes the jungle plants purify the polluted topsoil, producing clean water, which remains hidden underground.

Nausicaä and Asbel return to Pejite, destroyed after insects are lured from the Sea of Decay to attack the occupying Tolmekians. The Pejite survivors, on a single airship, reveal that they will do the same thing in the Valley to recapture the Giant Warrior. The Pejite prevent Nausicaä from alerting the Tolmekians by taking her captive, and knocking out Asbel when he attempts to help her. Later, the airship falls under attack by Tolmekian forces, and Asbel assists her in fleeing, while the timely intervention of Yupa helps to stave off any pursuit on the part of either the Pejites or the Tolmekians. While flying home to the Valley, she encounters a herd of enraged Ohmus following a baby Ohmu being used by the Pejites to lure the herd to the Valley. Nausicaä releases the baby Ohmu and gains its trust.

Meanwhile, the Tolmekians try to stop the herd with armored vehicles, but fail. Kushana arrives with the Giant Warrior to stop the Ohmu, but the Warrior is unsuccessful. The Warrior dies during the fight because it was awakened too early from its larval stage.

Nausicaä and the baby Ohmu arrive and are overrun as they attempt to calm the enraged Ohmu. The Ohmus then calm down and use their tentacles to revive Nausicaä. Everyone sees that Nausicaä's dress is stained blue with blood of the baby Ohmu, meaning Nausicaä must be the blue savior sought by Yupa. The film ends with scenes of people and insects living together in peace.

Vstop prost za člane MCja.