"Genma Wars: Eve of Mythology" is a supernatural action anime set in a world where ancient mythological forces collide with modern society. The narrative centers on a young man named Ryu, who becomes entangled in a centuries-old conflict involving the Genma, powerful demonic entities sealed away by an ancient civilization. These beings, once worshipped as gods, are now awakening and threatening to plunge the world into chaos. Ryu discovers he is the reincarnation of a legendary warrior tasked with preventing the Genma from regaining their full power.

The story begins with Ryu living an ordinary life until he encounters a mysterious woman named Aya, who reveals his true heritage and the existence of the Genma. Aya, a member of a secret organization dedicated to combating the Genma, guides Ryu as he begins to unlock his latent abilities. Together, they embark on a journey to locate and destroy the Genma's seals before they can fully awaken. Along the way, Ryu meets other individuals connected to the ancient conflict, including allies who share his mission and adversaries who seek to exploit the Genma's power for their own ends.

As the plot unfolds, Ryu learns about the mythology surrounding the Genma and the ancient civilization that once thrived. The Genma are not merely malevolent forces; they represent primal aspects of nature and human emotion, making their defeat a complex moral challenge. The series explores themes of destiny, sacrifice, and the duality of power, as Ryu grapples with the responsibility of his role and the potential consequences of his actions.

Key characters include Ryu, the reluctant hero burdened by his past life's legacy; Aya, the enigmatic and skilled warrior who serves as his mentor; and Kyo, a rival with a personal vendetta against the Genma. The antagonists are led by a shadowy figure known as the Dark Priest, who seeks to resurrect the Genma to reshape the world according to his vision. The interplay between these characters drives the narrative forward, with alliances and betrayals adding layers of tension.

The anime blends intense action sequences with moments of introspection, as the characters confront their fears and desires. The stakes escalate as the Genma grow stronger, culminating in a climactic battle that tests Ryu's resolve and the bonds he has formed. The series concludes with a resolution that ties together the mythological elements and character arcs, leaving room for interpretation about the future of the world and its inhabitants.