A toxic, ever-evolving alien life-form from the Dark Gaseous Nebula arrives to consume rampant pollution, and neither Humanity nor Godzilla may be able to stop it.

Coming to Earth on a meteorite that falls to Earth, a microscopic alien life form later named Hedorah feeds on Earth's pollution and eventually grows into a gigantic, ever-evolving, poisonous smog-spewing and acidic sludge-secreting monster. Godzilla, Earth's defender, senses the threat and meets ''the Smog Monster'' head-on in a literal battle for Earth's survival.—Thomas ''The Oldschool Hero'' Cianci

A pollution-eating monster named Hedorah comes from outer space. First it terrorizes the sea, then it goes on land where it encounters the Big G. After its fight with Godzilla it retreats, only to reappear again in a flying form that starts to kill people. Then it takes on its final form and that is when the Big G comes in again, and so the battle that will decide the fate of the world begins.—Spaceroach

By this time Godzilla, now the defender of the Earth, has become a national phenomenon just like the Loch Ness Monster in Scotland and, especially with children, ingrained into the Japanese consciousness. However, the Japanese still do not realize that destroying Earth will summon the millennia-old protector. A young boy finds a dangerous alien monster feeding on pollution that he names Hedorah, a pun on "hedoro", the Japanese word for pollution. In his dreams, he wishes for Godzilla to destroy Hedorah and, hopefully, persuade people to stop polluting Earth. Godzilla, coincidentally, fights the monster because of the destruction of the environment.—Anonymous