"Hades Project Zeorymer" is a four-episode OVA series that blends mecha action with psychological drama and political intrigue. The story centers on Masaki Kihara, a high school student who is revealed to be a clone of the original designer of the advanced mecha, Zeorymer. Masaki is forcibly recruited by the secretive organization Hades to pilot Zeorymer, a powerful weapon designed to dominate the world. The narrative explores themes of identity, free will, and the consequences of human ambition.

The series is set in a world where Hades, led by the enigmatic Kuromado Tokisada, seeks to overthrow the existing world order using Zeorymer. Masaki struggles with his role as a pawn in this grand scheme, grappling with the realization that his memories and personality are artificial constructs. As he pilots Zeorymer, he faces off against the Great Four, a group of elite mecha pilots loyal to the current world government. Each battle forces Masaki to confront his own humanity and the ethical implications of his actions.

Key characters include Kuromado Tokisada, the mastermind behind Hades, who manipulates Masaki and others to achieve his vision of a new world order. Miku Himuro, a Hades operative, serves as a confidante and emotional anchor for Masaki, though her own motivations remain ambiguous. The Great Four, consisting of skilled pilots like Gernia and Garan, provide formidable opposition, each with their own tragic backstories and personal stakes in the conflict.

The plot unfolds through a series of intense mecha battles, interspersed with moments of introspection and character development. Masaki's journey is marked by a growing awareness of his own agency, culminating in a climactic confrontation that challenges the very foundations of Hades' plans. The series concludes with an open-ended resolution, leaving the ultimate fate of its characters and the world they inhabit open to interpretation.