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The creature is never given a name in the comic itself. The name "Nuclear Reactor Demon" comes from the fact that the creature is a demon, and that it makes its first appearance by bursting out of a nuclear power plant.
The demon resembles a mass of tumorous organs with a number of entrail-like tendrils that it uses to attack. It has a large number of pure black eyes, a minimum of 21.
The Nuclear Reactor Demon appeared in Hell after Godzilla arrived at one of Hell's 'cities'. As Godzilla wandered the desolate landscape, he came upon a nuclear power plant. Godzilla approached the cooling towers, and peered into them. Shortly afterwards, the Nuclear Reactor Demon burst out of the cooling towers and attempted to attack Godzilla. However, Godzilla killed the demon by stomping on it multiple times.