In Godzilla vs. Destoroyah, the monster Destoroyah is formed from the cellular remains of the original Oxygen Destroyer, which had been used to kill the original Godzilla in 1954. The creature quickly grows in size and power, and is able to destroy buildings with ease.
Meanwhile, Godzilla has been experiencing a rise in his internal heat levels, which threatens to bring about a catastrophic nuclear meltdown. It is revealed that this is due to the fact that Godzilla's body was formed from the same radiation that created the original Godzilla, and is now reaching critical mass.
As Destoroyah continues to wreak havoc on Japan, a team of scientists races to find a way to stop Godzilla's meltdown before it destroys everything in its path. They eventually come up with a plan to freeze Godzilla's heart, thereby slowing down the nuclear reaction and preventing a meltdown.
However, this plan is complicated by the presence of the powerful and aggressive Destoroyah, who is determined to kill Godzilla and become the new King of the Monsters. The two beasts engage in a fierce battle, leading to a dramatic climax in which Godzilla's fate hangs in the balance.