"The Cain Saga" is a manga series that serves as a prequel to "Godchild," both written and illustrated by Kaori Yuki. The story is set in 19th-century England and revolves around the aristocratic Hargreaves family, particularly focusing on the enigmatic Earl Cain C. Hargreaves. Cain is a young, brooding nobleman with a tragic past, marked by the mysterious deaths of his parents and the dark secrets surrounding his lineage. His life is intertwined with his loyal servant, Riff, who acts as both a protector and a confidant.

The narrative delves into themes of family, betrayal, and the supernatural, often exploring the psychological and emotional turmoil of its characters. Cain's journey is driven by his quest to uncover the truth behind his family's cursed history, which involves a series of gruesome murders, forbidden love, and occult practices. The series frequently employs gothic and Victorian aesthetics, with intricate plotlines that blend mystery, horror, and romance.

Key characters include Cain's half-sister, Mary Weather, whose tragic fate is central to the story, and Dr. Jizabel Disraeli, a sinister figure with a personal vendetta against Cain. The series also introduces other members of the Hargreaves family, whose lives are entangled in the same web of deceit and tragedy. Each arc typically revolves around a new mystery or revelation, gradually unraveling the complex relationships and dark secrets that define Cain's world.

The manga is structured into multiple interconnected arcs, with each contributing to the overarching narrative of Cain's struggle against his family's cursed legacy. The storytelling is dense and layered, often requiring close attention to detail as it weaves together past and present events. The series is notable for its intricate character development and the moral ambiguities that challenge the protagonists, making it a compelling exploration of human nature and the consequences of inherited sin.