Eira was one of the many Chosen captured by the Red Wizards of Thay and transported to the Doomvault dungeon for experiments. More specifically, she was the chosen of Rillifane Rallathil, a minor god of the Seldarine. In one of the experiments, Eira was infused with the essence of a sacrificed Chosen of Talona, a process that left Eira with half of her life energy.
Eira was freed from her chains by the heroes of Daggerford and she asked to join them in the fight against the Thayans. However, in battle, there was a 50% chance that she would manifest the Talona side and fought with no concern for her own safety.