For many years, Eris served as an assistant to Rezo, helping him research a cure for his blindness and perform miracles. Eventually she fell in love with him, but whether or not he returned her feelings is unknown. At some point during this time, she helped Rezo to create a clone of himself, called Copy Rezo.

Desperate to cure his eyes, Rezo abandoned Eris to find the Philosopher's Stone. A few months later, Eris learned that he had been killed by Lina Inverse, Gourry Gabriev, and Zelgadiss Graywords. However, at the time she did not know that Rezo had a fragment of Ruby Eye Shabranigdu sealed inside him, and that Lina, Gourry, and Zelgadiss had killed Rezo to destroy that piece after it had been resurrected.

Nevertheless, grieving and angry over Rezo's death, Eris used Copy Rezo to issue a bounty on the three of them in the late Red Priest's name, as well as hiring the bounty hunter Zangulus and creating numerous other Copies, named Vrumugun (in the novels she sent Rahanimu and Dilgear along with Vrumugun). She planned to use the bounty to bring Lina, Gourry, and Zelgadiss to Sairaag, where she could take revenge on them. However, Copy Rezo betrayed her before she could do so. Before her death, she realized too late that no matter how hard she tried that she should have known that Copy Rezo wasn't really the real Rezo. Copy Rezo than blasted her into oblivion, leaving no remains behind.

In the manga, Eris only appears in flashbacks, as the manga shows that Copy Rezo already killed her before the Slayers even arrived in Sairaag.

Eris' full name is mentioned only in the light novels.

(Source: KanzakaDex, edited)