"De:vadasy" is a science fiction anime series set in a dystopian future where humanity is on the brink of extinction due to a catastrophic event known as the "Collapse." The Collapse unleashed a wave of destructive energy, rendering much of the planet uninhabitable and giving rise to monstrous entities called "Vadasy." These creatures, born from the corrupted remnants of human technology and biology, roam the wastelands, preying on the few remaining survivors.

The story centers on a group of genetically enhanced warriors known as "De:vadasy," who are humanity's last line of defense against the Vadasy threat. These warriors are created through a controversial process that fuses human DNA with advanced nanotechnology, granting them extraordinary abilities but at the cost of their humanity. The protagonist, Akira, is a young De:vadasy soldier who struggles with the ethical implications of their existence and the loss of their memories from before the transformation. Akira's journey is driven by a desire to uncover the truth behind the Collapse and the origins of the Vadasy, as well as to find a way to restore humanity's future.

As the series progresses, Akira and their comrades face increasingly dangerous Vadasy, each encounter revealing more about the creatures' connection to the Collapse and the shadowy organization responsible for creating the De:vadasy program. The narrative explores themes of identity, sacrifice, and the consequences of unchecked technological advancement. Key characters include Rina, a fellow De:vadasy with a mysterious past; Dr. Kurosawa, the scientist who oversees the program and harbors secrets about the Collapse; and Commander Haruto, a hardened military leader who questions the morality of using the De:vadasy as weapons.

The plot is structured around episodic missions interspersed with overarching revelations about the world and its history. As Akira delves deeper into the mysteries of the Collapse, they uncover evidence of a conspiracy that implicates the very organization they serve. The series builds toward a climactic confrontation that forces Akira to make a choice between their loyalty to humanity and their own sense of justice. "De:vadasy" combines action-packed sequences with introspective moments, creating a narrative that balances spectacle with philosophical inquiry.