A vampire with a death wish and a priest who wants to live meet in Yokohama. This vampire, known as Bloody Mary, is unlike any other: he can walk in sunlight, casts a reflection, refuses to drink blood, and has spent four hundred years unable to die despite every attempt. His red hair and red eyes mark him, but his true nature is a mystery even to himself, as he has no memory of his past. The priest is Ichirou Rosario di Maria, a high school student from a lineage of exorcists, who inherited the Blood of Maria—a powerful essence that vampires crave and that is said to be the only thing capable of permanently killing an immortal. Because of this blood, Ichirou is constantly attacked by other vampires.

When a group of vampires ambushes Ichirou, Bloody Mary rescues him and immediately begs him, calling him Maria, to end his endless existence. Ichirou is confused and skeptical, as he has no idea how to use his inherited powers. Bloody Mary explains that he mistook Ichirou for Isaac Rosario di Maria, a legendary exorcist from four hundred years ago who possessed the same cross-shaped rosario and the ability to destroy vampires. Realizing that Ichirou is merely a descendant, Bloody Mary proposes a pact: if Ichirou will dedicate himself to finding a way to kill him, Bloody Mary will protect Ichirou from all vampire threats until that day comes. Ichirou, desperate to survive, agrees and renames the vampire Mary.

The story unfolds as Mary and Ichirou navigate a world filled with hostile vampires, secret organizations, and the tangled history of the Rosario di Maria family. Ichirou struggles to unlock his dormant exorcist abilities, while Mary’s tragic past slowly resurfaces, revealing the origins of his immortality and the reason for his inability to die. Their bond deepens as they face enemies such as Hydra Scarlet and other vampire factions, and encounter allies like the exorcists Shinobu and Shion Yuuki. Key narrative arcs include the revelation of Mary’s human life in England four centuries ago, where he was a mortal boy dying of an incurable disease, and the desperate act of his lover—a woman also named Mary—who turned him into a vampire to save him, only to curse him with eternal life. The search for the original Isaac Rosario di Maria and the true nature of the Blood of Maria drives much of the plot, culminating in a confrontation that forces both Mary and Ichirou to decide what they truly want: death, life, or something in between.