"Code:Realize" is an anime adaptation of the otome visual novel of the same name, set in a steampunk-inspired alternate version of 19th-century Europe. The story centers on Cardia Beckford, a young woman whose body secretes a deadly poison, rendering her touch fatal to others. Isolated and feared, she lives under the control of her father, Isaac Beckford, a scientist who created her as a "horologium," a living weapon. When the British government attempts to capture her, she is rescued by Arsène Lupin, a charismatic gentleman thief. Lupin takes her to London, where she begins a journey to uncover the truth about her existence and her father's intentions.

Cardia joins forces with Lupin and a group of extraordinary individuals, each with their own motivations and secrets. The group includes Impey Barbicane, an eccentric inventor; Victor Frankenstein, a kind-hearted alchemist; Saint-Germain, a mysterious nobleman; and Van Helsing, a brooding vampire hunter. Together, they navigate a world filled with intrigue, danger, and political machinations, pursued by both the British government and a shadowy organization known as Twilight. As they travel across Europe, they uncover fragments of Isaac's research, which hints at a catastrophic event tied to Cardia's origins.

The narrative explores themes of identity, humanity, and redemption, as Cardia grapples with her nature as a weapon and her desire to live a normal life. The relationships between the characters deepen as they confront their pasts and work toward a shared goal. The story builds toward a climactic confrontation with Isaac, whose grand plan threatens the stability of the world. Through alliances, betrayals, and sacrifices, Cardia and her companions must decide what they are willing to fight for and what it means to be truly human. The series blends action, romance, and mystery, offering a compelling tale of self-discovery and camaraderie.