Bloody, an immortal vampire with red hair and red eyes, has spent four centuries searching for Maria, the legendary exorcist whose blood can finally grant him the death he desperately craves. Unlike other vampires, Bloody can walk in sunlight, casts a reflection, and refuses to drink human blood. His search leads him to Yokohama, where he rescues a young priest named Ichirou Rosario di Maria from a group of vampires drawn by the irresistible scent of the Blood of Maria flowing through Ichirou’s veins. Ichirou is a seventeen‑year‑old student and a descendant of the famed exorcist Isaac Rosario di Maria, but he has no knowledge of how to activate his inherited powers or kill vampires. Mistaking Ichirou for the original Maria, Bloody begs the boy to end his immortal life. When Ichirou proves unable to do so, the two strike a deal: Bloody, renamed Mary by Ichirou, will act as his bodyguard and protect him from the vampires who hunt him for his blood, while Ichirou searches for a way to fulfill Mary’s death wish.

The story unfolds in a modern Yokohama haunted by vampire clans and supernatural threats. Ichirou and Mary navigate a fragile alliance as they face a series of adversaries, each with their own connection to the Blood of Maria and to Mary’s forgotten past. Mary has no memory of his life before becoming a vampire, and his true origin becomes a central mystery. Along the way they encounter allies and enemies such as the vampire Hydra Scarlet, the exorcist Shinobu Yuuki, and other figures bound to the legacy of the Maria bloodline. Ichirou gradually learns to wield the power of the rosario he inherited, while Mary struggles with his own nature and the growing bond between them.

Notable narrative arcs include the investigation of Mary’s amnesia and the revelation of the original Isaac Rosario di Maria’s relationship with the vampire, the political clashes among vampire factions in Yokohama, and the ethical questions surrounding Ichirou’s promise to kill someone who has become his protector and friend. The story balances horror elements with moments of dark comedy and a slow‑burn emotional connection between the two main characters, all set against a backdrop of Gothic architecture and nocturnal cityscapes. The manga concludes with the resolution of Mary’s past and the fulfillment—or transformation—of the pact that first brought them together.