Prequel to .

With its flickering streetlights, moldy back alleys, and noisy populace, the Second Kowloon Walled City, despite the squalor of its already-demolished predecessor, evokes a special kind of nostalgia that its residents find endearing. Amidst the walls of this fading yet beloved landscape lives Reiko Kujirai, a 32-year-old realtor deeply in love with her coworker, Hajime Kudou, who is two years her junior. Though they have their differences, the two get along well enough to experience the joys of the walled city together. However, everything starts to fall apart when Kudou, half-asleep, suddenly kisses Kujirai—seemingly reciprocating the feelings she has yet to confess. But when Kudou explains that he had mistaken her for someone else, Kujirai finds herself drawn into a series of events that lead her to a past she cannot remember.

Queen Victoria of England has ordered her loyal watchdog, 13-year-old Earl Ciel Phantomhive, to investigate a series of suspicious deaths in southern Germany. Across multiple villages, all the victims have one thing in common: they had entered the so-called Werewolves' Forest right before they developed strange deformities and subsequently died. The rumors put blame on a "witch's curse," the nearby villagers' firm belief based on old folklore. Unconvinced that anything truly supernatural is at play, Ciel and his contracted demonic butler, Sebastian Michaelis—along with the rest of the Phantomhive servants—come across an isolated village in the Werewolves' Forest. Its residents are only women, hostile toward the outsiders and serving a young girl with emerald eyes and bound feet, Sieglinde "Green Witch" Sullivan. Ciel and Sebastian investigate to uncover the truth, but as they soon fall victim to the curse themselves, it appears that there is more to the local myths than meets the eye.

A young Taiwanese assassin codenamed "Glass Heart" committed suicide by jumping off a building, and her heart was pierced by metal fence. Miraculously, her life was saved by heart transplantation. During her recovery she began to experience strange dreams, which lead her to Japan looking for the donor of her heart, who happens to be Kaori Makimura, former partner of City Hunter Ryo Saeba. The author mentioned in the first tankoubon volume that Angel Heart only shares the same characters of City Hunter but not its continuation. The events are all parallel universe, therefore it has nothing to do with City Hunter.