The youngest of the Nifl royal family, Ylgr enjoyed a peaceful life with her family until the neighboring kingdom of Múspell invaded, resulting in the death of her mother and her separation from her family. Despite managing to survive, Ylgr is captured by Múspell and is watched by Helbindi, a high ranking officer of the Múspell army.
She is initially shown inside the Fortress of Cinders, calling out for her brother and sisters and refusing to eat, but after listening to Helbindi, he convinces her to start eating again. Ylgr senses that Helbindi is a nicer person than he lets on.
Later on, as a result of the arrival of the Order of Heroes, while Helbindi prepares to hand her over to the castle by one of his men on Surtr's orders and he talks about his life in Múspell, she realizes that he has a younger sister. After the Order of Heroes defeats Helbindi, Ylgr appears before them, having escaped the Múspell army. Just as Fjorm introduces the Order to her, a coughing fit comes over her. Ylgr offers to heal her and demands that she accompany them on the rest of their journey, feeling safer if she is with them, especially when she somehow knows the Summoner's name. While Fjorm and Alfonse express their doubts, Sharena convinces them to let her stay with them and the Order proceeds farther into the kingdom.
In Chapter 12, it is revealed that the Ylgr following them was the "traitor" within the Order, being actually Loki in disguise, who, after Alfonse and the Summoner revealed the truth, informed them that the real Ylgr was still imprisoned alongside Veronica, where they will be both sacrificed for the Rite of Flames. However, both princesses were rescued by Helbindi, who then told them to run away while he holded Surtr off. Unfortunately, Veronica and Ylgr were caught by Laevatein.