Trinity Blood unfolds on a ruined far-future Earth after Armageddon, where humanity struggles to survive in the shadow of the vampire Methuselah. The Methuselah are aligned with the New Human Empire, while the Terrans are protected by the Vatican Papal State, and both sides cling to a fragile peace that extremists repeatedly try to break. Terrorist attacks, political provocations, and hidden agendas push the continent toward renewed war, forcing the Vatican to rely on its AX unit to contain the violence and expose the conspiracies behind it.
At the center of the conflict is Father Abel Nightroad, a cheerful priest whose easygoing manner hides lethal combat skills, and Sister Esther Blanchett, a compassionate young nun who becomes his partner in the field. Together they move through ruined cities, secret alliances, and shifting loyalties, where every mission can alter the balance between the two races. With its blend of action, fantasy, and political tension, Trinity Blood follows characters trying to protect a peace that may collapse at any moment while older hatreds and fresh ambitions keep pulling the world back toward open conflict.