"Dark Edge" is a supernatural horror manga that centers on a high school student named Hikaru Takashiro, who becomes entangled in a dark and violent world after encountering a mysterious girl named Rei Ayanokouji. Hikaru’s life takes a drastic turn when he discovers that Rei is a "Shinma," a demonic entity that feeds on human blood. Despite her dangerous nature, Hikaru forms a bond with Rei, driven by a mix of curiosity, empathy, and a desire to protect her from those who seek to destroy her.

The narrative unfolds as Hikaru learns about the existence of the "Edge," a supernatural realm where Shinma originate. This realm is connected to the human world through a series of portals, and its influence begins to seep into Hikaru’s reality, bringing chaos and death. Rei, though a Shinma, is unique in her ability to resist her predatory instincts, making her a target for both humans and other Shinma. Hikaru’s connection to Rei draws him into a conflict involving the "Edge Keepers," a secretive organization dedicated to eradicating Shinma and sealing the portals to the Edge.

As the story progresses, Hikaru and Rei navigate a treacherous landscape filled with morally ambiguous characters, including other Shinma with their own agendas and Edge Keepers who are willing to sacrifice innocents to achieve their goals. The manga explores themes of identity, morality, and the blurred line between humanity and monstrosity. Hikaru’s journey is marked by his struggle to reconcile his growing feelings for Rei with the horrific consequences of her existence, while Rei grapples with her dual nature and the possibility of redemption.

The plot is driven by a series of escalating confrontations, both physical and emotional, as Hikaru and Rei face off against increasingly powerful adversaries. The manga’s tone is dark and intense, with graphic depictions of violence and a pervasive sense of dread. Key characters include Hikaru’s classmates, who become unwittingly involved in the conflict, and members of the Edge Keepers, whose motivations and methods are often as monstrous as the creatures they hunt. The story builds toward a climactic confrontation that forces Hikaru and Rei to confront the true nature of their bond and the consequences of their choices.