Eua is a mysterious and powerful being who appears as a central figure in Higurashi: When They Cry GOU, acting as the catalyst for the series' tragic events. She is a woman with a regal and otherworldly appearance, characterized by long purple hair styled in a hime cut and a pair of distinctive silver, horseshoe-shaped horns that float on either side of her head. Her attire consists of a shrine maiden outfit complemented by a green sash adorned with a large medal, and she carries a shakujou, a traditional Buddhist ringed staff, which she often manipulates telekinetically.

Eua's personality is defined by an ancient, cosmic-level boredom born from near-omniscience and omnipotence, which has caused almost all acts of creation to lose their meaning for her. To escape this tedium, she seeks entertainment in the form of fragment games, observing the struggles and suffering of lesser beings. She speaks in a condescending and archaic manner, often referring to humans as child of man, and has a tendency to laugh and giggle with twisted satisfaction when she is particularly amused, especially by the actions of Satoko Hojo. Despite her cruel enjoyment of others' pain, she maintains a nonchalant and almost playful demeanor, showing little concern even when facing defeat.

In the story, Eua's primary role is that of an enabler and an observer. She is the one who bestows upon Satoko Hojo the power to loop through time and travel between fragments. Eua first appears to Satoko after the girl touches a horn-shaped object inside the ritual warehouse at the Furude Shrine, transporting her to the Sea of Fragments. Recognizing Satoko as an old friend from another world, she grants her wish to create a world where Rika Furude would never leave her, providing her with the looping ability while stipulating that she must die for it to work and that her actions must serve as entertainment. Eua watches these loops with great interest, offering occasional explanations and warnings, such as the irreversible nature of accumulated memories and the risk that dying before Rika would lead to a fragment where Rika never existed. She is directly responsible for escalating the conflict between Rika and Satoko, referring to Rika as her cat.

Eua's key relationships are with the two main characters of the arc. She is deeply fond of Satoko, whom she addresses by other names like Vier and Mitsuyo, implying a forgotten history spanning millions of years. She derives immense entertainment from Satoko's descent into villainy and actively supports the creation of her witch half. Her relationship with Hanyuu is antagonistic and reveals much about her nature. Eua refers to Hanyuu as her failure and a part of her, implying she is the original or perfect version from which the flawed Hanyuu was created. When Hanyuu appears to interfere, Eua effortlessly overpowers her, traps her, and cruelly forces her to witness Satoko's brutal torture of Rika, taking great pleasure in Hanyuu's despair.

Eua shows little to no development throughout the narrative, remaining a static force of nature whose motives are consistently driven by the search for amusement. Her true nature and origin remain enigmatic, though she is identified as a supreme being whose power is nearly limitless, reaching the level of omnipotency and omnisciency. Her notable abilities are vast and terrifying. She can grant humans the power of time looping without the imperfections of Hanyuu's version, allowing them to retain all their memories across fragments. She demonstrates telekinesis by controlling her staff and other objects, can conjure powerful energy blasts, create bindings to restrain others, manipulate the environment, and easily overwhelm even powerful beings like Hanyuu, whom she traps and forces to watch specific fragments.