'Robe worn by the Omenkillers, butchers of twisted conscience. Its thick apron is worn in remembrance of Rollo, the progenitor of the Omenkillers and a perfumer of antiquity.' The Omenkillers are the canon's most loathed institutional caste : an order of butchers paid by the Erdtree's nobility to euthanize Omen children at birth, before the children's horns can grow long enough to require ritual cutting. Omen are the canon's Crucible-corrupted demigods, children born with the primordial signs of the Erdtree's first form (horns, tails, feathers), who, in the Erdtree's purified order, are seen as defective and disposable. The Omenkillers were drafted from the perfumer guild during the early Erdtree's first generation, when their sleep-and-pain mixtures were repurposed for euthanasia. Rollo, the named progenitor, was a perfumer who agreed to the new vocation. His apprentices kept the apron.

'The blade of this huge, loathsome cleaver comprises a row of amputated Omen horns. Weapon of slaughter wielded by Omenkillers. The hideous horns cause blood loss, adding vibrant colors to the ongoing pageant of butchery.' The Omenkillers' weapons are their own indictment : a cleaver made from the horns of children they killed, polished smooth from continued use, used to kill the next child. Their crime is what the Erdtree's order specifically required to keep itself pure : the canon's Mohg and Morgott are Omen demigods who escaped this fate (because Marika could not be seen to kill her own demigod children) and who carry, in adulthood, every grudge of every child the Omenkillers DID kill. The two brothers' separate revolts are written in their unkilled names.