"Castlevania: Curse of Darkness" is a manga adaptation of the video game of the same name, set in the dark and gothic world of the Castlevania franchise. The narrative centers on Hector, a former Devil Forgemaster who once served Dracula but abandoned his allegiance after becoming disillusioned with the cruelty of his master's war against humanity. Following Dracula's defeat, Hector seeks a quiet life, but his past catches up to him when he is framed for the murder of his wife, Rosaly. Consumed by grief and a desire for vengeance, Hector embarks on a journey to uncover the truth behind her death.

The story unfolds in a world plagued by demons and supernatural forces, where Hector's unique ability to forge and command demonic creatures becomes both a weapon and a burden. His path crosses with Isaac, another Devil Forgemaster who remains loyal to Dracula's cause. Isaac harbors a deep hatred for Hector, viewing him as a traitor, and seeks to eliminate him. Their rivalry drives much of the conflict, as Isaac manipulates events to further his own agenda and undermine Hector's quest for justice.

Throughout the manga, Hector encounters a variety of allies and adversaries, including Trevor Belmont, a descendant of the legendary Belmont clan of vampire hunters, and Saint Germain, a mysterious traveler with his own enigmatic motives. The narrative explores themes of betrayal, redemption, and the consequences of wielding dark powers. Hector's journey is not only one of vengeance but also of self-discovery, as he grapples with his identity as a Devil Forgemaster and his responsibility for the chaos unleashed by his creations.

The plot is driven by a series of battles, both physical and ideological, as Hector confronts powerful foes and uncovers the machinations of those who seek to exploit the remnants of Dracula's legacy. The manga delves into the lore of the Castlevania universe, incorporating elements such as the Crimson Stone, a powerful artifact tied to Dracula's resurrection, and the intricate relationships between humans, demons, and those who bridge the two worlds. The story builds toward a climactic confrontation that tests Hector's resolve and forces him to confront the true cost of his actions.