The microscopic alien lifeform Hedorah feeds on Earth's pollution and grows into a poisonous, acid-secreting sea monster.
After it sinks an oil tanker and attacks Dr. Yano and his young son Ken, scarring them both, Hedorah's toxic existence is revealed to the public.
Ken has visions of Godzilla fighting the world's pollution, and insists Godzilla will come to humankind's aid against Hedorah.
Hedorah metamorphoses into an amphibian form, allowing it to move onto land to feed on additional sources of pollution.
Hedorah is confronted by Godzilla.
Hedorah is easily overpowered by Godzilla and retreats into the sea.
It returns shortly thereafter in a flying saucer shape demonstrating new, even deadlier forms which it can switch between at will.
Thousands of people die in Hedorah's raids and even Godzilla is overwhelmed by Hedorah's poisonous emissions.
As hope sinks, a party is thrown on Mt. Fuji to celebrate one last day of life before humankind succumbs to Hedorah.
Ken realizes that Godzilla and Hedorah have come to Mt. Fuji as well for a final confrontation.
Dr. Yano has determined that drying out Hedorah's body may destroy the otherwise unkillable monster.
The JSDF swiftly constructs two gigantic electrodes for this purpose, but their power is cut off by Godzilla and Hedorah's violent battle.
Godzilla energizes the electrodes with his atomic ray, dehydrating Hedorah's outer body.
Hedorah sheds this outer body and takes flight to escape, but Godzilla propels himself through the air with his atomic ray to give chase.
Godzilla drags Hedorah back to the electrodes and continues to dehydrate it until Hedorah dies.
Godzilla tears apart Hedorah's dried-out body and dehydrates the pieces until nothing remains but dust.
With Ken calling after him, Godzilla returns to the sea, but not before glaring threateningly at the surviving humanity whose pollution spawned Hedorah.
One of the good ones to watch but keep in mind it is in the 70s so it might be kind of different to you if you don't watch movies from that time.
Here's the trailer