The Blood Shadow is a world superficially identical to the “real” Earth.
The secret of the origin of the Blood is lost. Some claim that the Blood are the lost scions of Christ, or the children of the Nephilim. Others say they are the sons and daughters of ancient pagan gods. Some claim they are freak mutations, or genetically engineered by an advanced alien civilization.
However they came to be, it is clear that the Blood have been active since at least the Dark Ages. Some of the factions have records going back at least that far.
While many of The Blood operate independently, nearly all of them are at least watched by one of the major factions. These groups are composed of humans and Blood, working together with varying degrees of willingness. The factions generally look for other members of the Blood to recruit. Each of the factions has their own goals and ideas about what the Blood are, and what should be done with them. These purposes are often in conflict.
In addition to the major factions, there are small enclaves scattered around the globe. There are rumours of a clan of Blood assassins operating out of Japan, and others about a temple of Blood monks hidden from the Chinese government in Tibet.