Nausicaä of the Valley of the Wind is a film by Hayao Miyazaki based on a manga by the same name. The film was released originally in 1984 and whilst it was created before the formation of studio Ghibli it is considered by its founders to be the beginning of the studio.
Nausicaä of the Valley of the Wind's story takes place in the far future where man has destroyed the Earth in the "Seven Days of Fire". Now, all that are left are small pockets of survivors. One group of these survivors resides in the "Valley of the Wind". Ruled by King Jil, this group of survivor's attempts to defend the valley from the sea of decay (Also known as the toxic jungle). Meanwhile the Princess Nausicaa feel's compelled by a need to understand the toxic jungle and discovers that the toxic plants are purifying the world, not poisoning it.