Emrilia Herkaaze was recruited from a world in the Belladone Reach by the Silent Sisterhood. She met Amendera Kendel in the hold of the Black Ship and the two became friends during their aspirant trials.
At some point Herkaaze and Kendel encountered a fire-witch on Sheol Trinus. Unwilling to fall back and regroup, Herkaaze was struck by burning debris that blinded her left eye and badly scarred her face. The friendship between the two soured afterwards as Herkaaze blamed Kendel for not supporting her.
During the Horus Heresy, Herkaaze was an Oblivion Knight in command of the Black Ship Validus when it went missing. The prisoners escaped and were able to survive as the Life-Eater failsafe had been sabotaged. It was located by Kendel, now also an Oblivion Knight, and they tracked down the psyker gestalt that had taken over the ship. After it claimed to be a future version of Leilani Mollitas, an aspirant accompanying Kendel, Herkaaze attacked the Mollitas of the present and killed her to end the threat before it began. Left alone with Kendel, Herkaaze broke her Vow of Tranquility, chastising Kendel for thinking that the message from the future was worth hearing and claiming only the God-Emperor had the right to change the course of history.
Herkaaze went on to become a Sister-Excruciatus. When Kendel returned to the Somnus Citadel as Malcador's Agentia Tertius, Herkaaze met her and called her oath-breaker, saying that she shamed her cadre and ought to have been executed. When presented with the sigil of the Regent of Terra, Herkaaze reluctantly allowed Kendel to see the Seventy.
Emrilia Herkaaze had a topknot of rust-red hair and wore lightning bolt symbols on her shoulders as a mark of rank. Her left eye was replaced by a blue augmetic. After becoming a Sister-Excruciatus she wore a heavy necklet and black steel torcs on her arms.