Birna was a Danish Viking warrior who served as an advisor to Jarlskona Soma during the late 9th century AD. Birna originally worked as a smuggler in both Scandinavia and England, and she had a nihilistic outlook on life both before and during her service under Jarlskona Soma. In 873 AD, she was taken prisoner by Anglo-Saxon rebels loyal to Ealdorman Wigmund of Cambridge at Gratian's Villa in Cambridgeshire, but she was rescued when Soma and Eivor slew the guards. Birna told Soma of her plans to turn Gratian's Villa into a homestead, but Soma convinced her to lead the fellow prisoners back to her camp and join her for the assault on Cambridge when the time was at hand. Eivor initially suspected Birna of being the traitor that Soma had been searching for, as Birna had fallen from grace with Soma and had shown resentment towards Galinn, whom Eivor had initially thought was the most trustworthy lieutenant. However, after further investigation, Eivor revealed Galinn as the traitor before Soma, and Soma then executed Galinn in front of Birna and Lif, who were ordered to dispose of his body. Eivor, Lif, Birna, and Soma then killed Wigmund at the Battle of Ely, finishing him off. Before Eivor could bid farewell to Birna, she said that she had no future in Cambridge since she had fallen from grace with Soma, and she instead volunteered to live among Eivor's Raven Clan and join his crew. Eivor welcomed her, and she became one of his companion warriors and rowers.