Supernatural beings known as Darkstalkers envelope the Earth in darkness, leaving the human population starved and powerless. Resentful of Darkstalker rule, humans prepare to revolt against Demitri, the Darkstalker vampire ruler of Earth banished from the Demon World, who is planning on a revolution of his own against the Demon World to regain his place in it. The powerful succubus Morrigan, a member of the Demon World's ruling clan, impedes his efforts. But when an army of mysterious robots descends upon Earth, the two enemies unite in the face of a common foe.

Elsewhere, in a rural town, a girl named Anita is saddled with rumors that she has survived repeated Darkstalker attacks. Fearful that her presence will attract Darkstalkers, paranoid villagers attack Anita. Donovan, a Darkstalker-hunting monk, rescues Anita but has to endure her hatred and his own self-loathing because he himself is half Darkstalker.

Donovan responds to a town's call for help, and is severely wounded in a fight with the demon-armor Hannya, who has been slaughtering the town's travelers. Anita selfishly refuses to tend to him. Mei-Ling and Hsien-Ko, two other demon-hunters, arrive and convince Anita to take care of him rather than relish in his defeat.

Elsewhere, the sun-entity Pyron descends to Earth, bent on destroying it. The Huitzil robots warn Pyron that Earth may pose a greater threat than he thinks -- the combined powers of Morrigan, Demitri, and, if he'd join them, Donovan would be enough to overpower even him. The planet-crushing Pyron delights in the fact that Earth's inhabitants will offer him resistance, for he so rarely encounters an opportunity to do battle with worthy opponents.

The humans mistake Pyron for the reappearance of the sun, and begin to celebrate the defeat of the Darkstalkers. Little do they know that they are about to face an enemy so powerful that only the Darkstalkers can save them. Pyron begins attacking the Earth, and his rampage slowly closes in on Demitri, reputed to be Earth's supreme fighter. As Pyron seeks out his opponent, Mei-Ling and Hsien-Ko tell Donovan and Anita of their childhood. They explain how their demon-hunting is part of an attempt to redeem the soul of their mother, lost centuries ago in battle with Darkstalkers. Collectively recognizing the threat Pyron poses, the foursome surmounts their personal issues and set out to do battle with him. Meanwhile, Morrigan begins to unravel the mystery behind the Huitzil robots, destroyers that knock down civilizations that get too advanced.

The Huitzil reveal their true program, and their ambiguous role in this cataclysmic clash becomes clear: they are neither Pyron's allies nor mindless eradicators of civilization. Rather, they are programmed to eliminate any and all warlike species on Earth -- and Pyron is now the greatest threat to Earth's peace. As Pyron begins to do battle, he proves that his skills live up to his reputation. Pyron takes on Demitri, and after administering him a brutal thrashing, he single-handedly destroys a small army of attacking Huitzil. Pyron's presence sparks anarchy in both the human and demon realms, and Morrigan must fight her way through dragon-demons in order to come to the aid of her former enemy, and now possible love interest, Demitri. Mei-Ling and Hsien-Ko make failed attempts to defeat the rampaging Pyron, as does a fully assembled Mega-Huitzil, and Donovan, who is mortally injured in the fight. Anita finally unleashes her awesome power and revives the blood-spattered Donovan, who then reaches inside himself for the strength to overcome his own self-loathing and defeat Pyron.