Yerma is a spear-wielder warrior that crosses paths with the Penitent One. She is a survivor of the events of Two Moons caused by the Miracle's will, which made people transform into horrible monsters, one of them being Svsona. Yerma reveals that it was actually Svsona who caused this event, due to her vanity and obsession with her own beauty, after praying to the Miracle that no one else could see her beautiful reflection on the lake. Because of this, Yerma is now on a quest to murder Svsona.
She is first encountered on Profundo Lamento, and gives the Penitent the Steely Battle Lance, allowing him to access the Weapon Memories and use the Marks of Martyrdom on his weaponry.
After this she will appear on other specific locations, offering her aid to defeat the following bosses: On Sacred Entombments, before fighting Great Preceptor Radamés, on Beneath Her Sacred Grounds, before fighting Afilaor, Sentinel of the Emery, on Two Moons, before fighting Svsona, Fermosa Fembra.
If Yerma's help is rejected she will permanently dissapear from the area, and won't be encountered until reaching the next the three mentioned bosses.
To complete her quest, the Penitent one must give Yerma the Holy Oil of Everlasting Anointment before entering the room above her, which contains the mirror that unlocks Svsona's bossroom, otherwise she will die. If the Penitent refuses to aid Yerma despite giving her the item, she will also perish.