When 's population drastically increased, humanity, led by the United Nations, attempted to colonize Mars. During the colonization, they discovered two alien technologies: the Bacillus virus and the Crusnik nanomachines. The colonists injected the Bacillus in their bodies which transformed them into a vampiric race known as "Methuselah". They installed the Crusnik in the bodies of four test tube babies: Seth, Cain, Abel and Lilith whose enhanced bodies were the only ones able to survive the procedure.
Continuing wars on Earth eventually led to Armageddon, the apocalyptic event that happened 900 years before the start of the story, and the colonists returned to Earth to help with rebuilding. However, when the colonists returned to Earth, a war broke out between the Methuselah and the humans who had remained on Earth. Abel, Cain, and Seth sided with the Methuselah—while Lilith supported the Vatican, which guarded humanity. During the war, Cain went insane and killed Lilith. In grief, Abel took her body to the Vatican where she was buried. Abel remained at her side, weeping for her, for 900 years.
At the start of the story, the Methuselah, still a major political and military force, continue to wage war on the "Terrans", as they call the human inhabitants of Earth. The Roman Catholic Church is a major military power determined to protect humans from the Methuselah, with its seat of power based in the Vatican. The Methuselah have their capital in Byzantium, which is surrounded by a field of particles to filter out UV radiation, protecting the Methuselah population.
Both groups use "lost technologies", such as airships, missiles, and computers, to engage in a cold war with one another. A third great power, Albion also plays a role in the war with its superior arsenal of lost technology and weapons and higher level of manufacturing ability versus the Vatican. The independent monarchy of Albion is a primarily human country, however the secret of their expertise in lost technology is found in the Ghetto, an underground city of enslaved Methuselah. It is these Methuselah who operate and manufacture the lost technology, but with the death of the Albion Queen, some of the enslaved vampires begin a rebellion for the freedom of all of the Ghetto residents.
Trinity Blood was originally a novel written by Sunao Yoshida. It was later on adapted as a manga by Kujyo Kiyo. The Trinity Blood animation series was announced in 2004, a few weeks before Sunao Yoshida tragically dies of lung blockage. He was only 34 years old.
Trinity Blood has been likened to many series with similar themes: Helsing (theme - doesn't help that the strong-willed Caterina looks a lot like the equally strong-willed Integra either), Trigun (protagonist - similar personality between Abel and Vash Stampede), even Final Fantasy (Zeppelin ship designs). Still, the series manages to give old themes entirely unique twists and making them their own. The music and soundtrack is beautiful, Crusniks entirely unique, awesome weaponry (blood scythe!), the protagonists lovable and some of the bad guys redemptive in the eyes of viewers.