Crona uses this form of magic in conjunction with their blood element affinity. This form of magic allows Crona to add extra effects to their blood.
Black Blood: The user manipulates their own blood, made black from the curse. The blood can be hardened or liquefied at will.
Black Sword (暗黒剤あんこくけん, Ankoku Ken): With an open grimoire, the user manipulates their own black blood to take the form of a long, large, black Scandinavian broadsword with a grey hilt, a white stripe down the middle and spikes around the guard.