Xenovia first appears in Volume 3 along with Irina under the order of the Church to retrieve the three stolen Excalibur swords. She and Irina formed a temporary alliance with Issei, Koneko, Yuuto, and Saji, in which they would retrieve the stolen Excaliburs fragments but would allow Yuuto to destroy one of them. During the fight with Freed Sellzen and Valper Galilei, she reveals herself to be the wielder of Durandal, and quickly turns the tide of battle by destroying the fused Excalibur and cutting down Freed. Following the battle with the Fallen Angel leader Kokabiel, she became a Devil under Rias after finding out that God died.
When Xenovia was first introduced, she was portrayed as an individual with a quiet and serious demeanor, putting her mission first and only speaking when necessary. She also prefers not to get involved in problems that do not concern her. While a faithful member of the Church, her beliefs are flexible enough to accept help from a Dragon such as receiving a free lunch (after Irina spent all their money on a fake painting of a Saint), and wanting to not only accomplish their mission, but survive afterwards as well. After Volume 3, she gains a very close relationship with Asia, being touched by her kindness and apologizes for calling her a witch when they previously met. Like Asia, as a person who was raised in the Church, she lacks common knowledge on the life of a normal person, evident when she brought a box of condoms to school.
As a Knight, Xenovia is able to move at superhuman speeds, which, combined with the destructive powers of Durandal, makes her a formidable fighter. She also has the ability to tap into Durandal’s holy aura with other swords, evident when she uses it with Issei’s Ascalon (Issei allows her to use it since he is not a good swordsman and because she cannot fully control Durandal).
After becoming a devil, Xenovia becomes obsessed with having Issei’s baby, since she figures that with Issei being host to the Red Dragon Emperor, his genes must be superior. Her reasons for this sudden desire is that as a holy sister, she had to live a life of complete celibacy, but now that she’s become a devil, she’s free to live the life of an ordinary woman, which in her mind means having babies, something she thought she’d never be able or allowed to do.
From Volume 19, she adopts her legal guardian’s family name, Quarta.