In "Bloody Mary," Ichirou Rosario di Maria crosses paths with Bloody, a vampire who defies typical vampire attributes. With crimson hair and eyes, Bloody does not drink blood or attack humans, and can even withstand sunlight. Their encounter happens when Bloody saves Ichirou from a group of vampires drawn to the rare "Blood of Maria" flowing in his veins—a trait that has repeatedly endangered him. After dispatching these attackers, Bloody begs Ichirou, whom he calls "Maria," to put an end to his immortal existence.
At first, Ichirou doubts that Bloody is truly harmless and cannot grasp how he could possibly kill such an apparently deathless being. The confusion arises because Bloody mistakes him for Isaac Rosario di Maria, a famed priest and exorcist from four centuries earlier. Ichirou carries a cross-shaped rosary handed down from his grandfather, which in theory should grant him the exorcist abilities needed to destroy a powerful vampire like Bloody, but he has no idea how to activate them.
Determined to withstand the constant attacks on his life, Ichirou strikes a deal with Bloody, giving him the new name "Mary." The agreement is that until Ichirou can fulfill Mary's wish for death, the vampire must offer unwavering protection to the human.