The Black Rage is a psychological and genetic affliction unique to the Blood Angels and the brotherhoods descended from their bloodline. Encoded within their gene-seed is the imprinted memory of their progenitor's final battle, a trauma so profound that it can surface in the minds of his descendants millennia after the events themselves.
When the Rage takes hold, an afflicted warrior loses the boundary between past and present, reliving the death of his ancestor as though it were happening to him. He becomes convinced that he stands upon that ancient battlefield facing the same foe, and is consumed by overwhelming grief and fury. In this state he fights with terrifying ferocity, heedless of danger or pain, but is largely lost to reason and unable to distinguish the true situation around him.
The onset can be triggered by the stress and carnage of combat, and it is regarded as a slow-burning doom hanging over every warrior of the line. Those who succumb are not cast out but honoured, gathered into a special formation and given the chance to spend their final fury against the enemy, seeking a meaningful death rather than a wasted one. To the Chapter, the Black Rage is at once a curse, a mark of kinship with their fallen father, and a grim inheritance that no cure has ever been able to lift.