Following the reunification with their lost Primarch Angron upon the world of Nuceria, the bloody-handed Primarch enacted many changes within the structure of the XIIth Legion. Knowing how successful his own cortical implants were at boosting a warrior's prowess in battle, Angron ordered his Apothecarion to insert the Butcher's Nails implants within every Astartes of the World Eaters Legion to enhance their aggression and pain tolerance far beyond that which even the gene-engineered flesh of a member of the Space Marine Legions was capable. Initially, this posed difficulties, as Angron's implants were relics of a long-lost technology, little understood even by their makers, while removing them from Angron for close study would have proven fatal to the Primarch. The Legion's Techmarines and