"The Sea of Corruption was the new world... An ecological system born in the polluted wastelands created by civilizations long past. Only the great insects could live among the giant fungi and the miasma they exhaled, and so the earth was slowly submerging beneath that decaying sea..." 
The Sea of Corruption is a vast poisonous forest that constantly threatens the thin areas where humans can live. The forest is filled with a deadly miasma that chokes all human and animal life. Only those wearing a Shohki Mask or the equivalent can hope to survive in this deadly place.
The Sea has several different layers. The "trees" of the forest release spores in the afternoon that cause updrafts in the air .
Insects like the Ohmu are unaffected by the miasma and when they travel out of the Sea of Corruption, they bring deadly spores that can easily take root in clean lands, which in turn spreads the Sea further. Most communities close to the Sea of Corruption have elaborate methods, including using Fire Wands, to prevent the spread of these deadly spores.
In the English dub of Nausicaa and the Valley of the Wind, it is referred to as the Toxic Jungle.
The Sea of Corruption has several layers or strata. The topmost and most poisonous is the Active Layer. The middle layer is still poisonous and is known as the Petrified Layer. The bottom is known as the Vaults. The air at this bottom layer is clear and there is no miasma.
The flora in the Sea of Corruption are made up of various fungi and nature that release deadly spores into a Miasma. The Sea of Corruption spreads whenever the spores manage to find a suitable location to take root, such as dead bodies. Infected locations will quickly be overrun with fungi and become part of the Sea if left unchecked.
There are two groups that interact with the Sea of Corruption on a near-daily basis: the Forest People and Worm Handlers. The Worm Handlers are seen as lowly outcasts by most other groups. As their name implies, they use worms from the Sea as tools for various purposes.
The Forest People, however, are a hidden group of humans who live in harmony with the Sea of Corruption. They craft suits and clothing from insect hide and are allowed to take some of the insect's eggs for food. The Forest People are revered by the Worm Handlers.
The Sea of Corruption is constantly spreading. Whenever insects become angered, they go on rampages and inadvertently spread the deadly spores that they carry with them. This causes clean lands to quickly become infected and overrun with poisonous fungi, converting it into part of the Sea of Corruption.
- DE 1a pg 24
- DE 1 pg 134
- DE 1 pg 27
- DE 1 pg 137
- DE 1 pg 126
- DE1 pg 436
- DE1 pg 41
- DE 1 pg 89
a See Page Conversions Between Editions to convert Deluxe Edition volume 1 (DE1) to other editions