Gillian is a middle-aged woman with a few lines around her mouth, and short, dark hair. Her outfit consists of a greenish-yellow shawl that she wears over a long-sleeved, white shirt, a full-length brown skirt, and brown sandals.
Before the events of Crisis Core -Final Fantasy VII-, Gillian, while working with Shinra's science department, met with Dr. Hollander and became a part of his experiment. While he was still in Shinra, Hollander was trying to surpass Professor Hojo by being the first to create a human with the powers of the Cetra. This experiment was named "Project Gillian". As a subject of this experiment, Gillian Hewley was infused with Jenova cells. When she became pregnant, the result was Angeal Hewley.
Another child, not born from Gillian, was also used in the experiment: It was the project that created Genesis Rhapsodos. In this case, Genesis was injected with Gillian's cells while a fetus; however, the experiment was imperfect. Genesis was the son of Banora's landlord.
Zack Fair would later be sent to investigate the hometown of both Genesis and Angeal, and would meet Gillian Hewley. Zack asks Gillian about Angeal's Buster Sword, which Angeal never uses. It is revealed the sword is a symbol of the family's honor, shedding new light on Angeal's earlier assertion to Zack that he does not want it to become rusty.
When Zack returns to Gillian's house a second time he finds Angeal standing over her lifeless body, having apparently killed her; this incident drastically changes the relationship between the two SOLDIERs. Gillian's body was most likely destroyed in the bombardment of Banora Village. Later, Zack discovers through Dr. Hollander and Angeal that Gillian committed suicide because the shame of participating in the experiments became too great.
The Crisis Core Complete Guide reveals that Genesis and Hollander left Gillian alive when they took over Banora because they wanted her aid in researching a cure for Genesis's degradation. However, Gillian refused to aid them, believing the experiment was a mistake. The developers state that it was not Gillian's cells Hollander and Genesis wanted, but her scientific knowledge, and deliberately refuse to say conclusively if Gillian would have known a way to cure Genesis.
In the English release of Crisis Core -Final Fantasy VII-, Gillian is voiced by Takayo Fischer.