The Intergalactic Alliance Empire, aiming to assert dominance over all beings in the universe, creates the most powerful assassin in history named Greylon Darwin. Possessing the unique ability to annihilate opposing forces, Greylon successfully executes various missions across many galaxies, including the destruction of demons, monsters, and even entire civilizations.

He earns the title of the God of Death after defeating the Supreme Shinigami in the Underworld. However, one day, he decides to leave the Alliance and start a new life as an ordinary person.

The Alliance is unwilling to let him go, but in an effort to avoid conflict, they agree to release Greylon after his one last mission. The Empire provides him with his own planet for a peaceful existence alone and signs a non-aggression treaty with him.

However, several years later, due to their own carelessness, the Alliance violates this treaty, thereby unleashing its own creation against itself. Now, the God of Death intends to seek revenge and destroy those who once created him.

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