Gillian Grayson was a student at the Jon Grissom Academy, and the adoptive daughter of Paul Grayson, a Cerberus operative and red sand addict. She showed promising biotic ability early on, and had high-functioning autism. Gillian was twelve during her time as a victim of a Cerberus operation and was likely exposed to element zero during the Cerberus-orchestrated industrial "accident" on Yandoa.
Gillian is described as tall for her age with dark hair. Due to her condition, she was prone to silence, and was highly sensitive to social interaction and physical contact, with occasional bursts of sociability. She was given to Grayson as a baby by Cerberus, in order for them to infiltrate the Alliance's premier biotics research program, the Ascension Project. She was considered the potential 'saviour' of humanity by the Illusive Man and her father alike, though it is possible the Illusive Man used this excuse to further enthrall her well-meaning father into deceiving his daughter and breaking Alliance law.
Mass Effect: Ascension
During her time at the Project, Gillian was drugged by Dr. Jiro Toshiwa, apparently in an attempt to increase her biotic powers. Deliberately or not, this medication might also have been responsible for worsening her autistic condition. The medicine had the desired affect on Gillian's biotic abilities, allowing her to throw a fellow student, Nick, twenty feet, cause chaos in the Academy cafeteria and unleash a high-level biotic singularity before Gillian was stunned by Hendel Mitra. When Dr. Toshiwa gave her a cerebrospinal dose of the medicine, Gillian suffered a seizure and was hospitalised.
After this, under the guise of a concerned parent, her father took her, Kahlee Sanders, and Hendel Mitra to Omega to "hide" her from Cerberus. His real intention was to hand Gillian over to his boss for further study and training. Unfortunately for him, Pel, her father's one-time partner, had revolted against Cerberus and intended to hand her over to the Collectors in exchange for valuable technology. Luckily, Lemm'Shal nar Tesleya, a quarian on his Pilgrimage, found them while searching for a fellow quarian and freed them from Pel's prison. Lemm took them to safety aboard the Migrant Fleet, but the three were isolated aboard their shuttle on the Idenna while the quarians debated what to do with them.
Gillian appeared to enjoy her time in confinement, and actually liked the quarian environmental suit she was asked to wear (to the extent it was a struggle to make her take it off). Kahlee speculated this might have been related to Gillian's autism and her reluctance to be touched. Meanwhile, Hendel took the opportunity to give Gillian one-on-one biotic tuition to improve her skill and control. Unfortunately, just as the quarians made their decision about what to do with them, the Idenna came under attack; Gillian's father had followed them to the Migrant Fleet with a squad of Cerberus commandos.
During the assault on the Idenna, Gillian was told to hide in Seeto'Hodda nar Idenna's quarters, but she became uncomfortable with the way everything had been rearranged and went back to the shuttle. She encountered several Cerberus operatives on the way, but with her abilities honed by Mitra, she was able to kill them with ease, even dropping a six-ton forklift on soldiers who tried to stop her. Her father managed to stun her, intending to take her back to Cerberus. However, Kahlee Sanders convinced him that Cerberus was trying to turn Gillian into a weapon, and that they had essentially been poisoning Gillian and making her condition worse, rather than turning her into a saviour.
Finally Grayson agreed to let her stay on the Flotilla to protect her from Cerberus which he no longer believed in, along with Hendel, who had formed a bond with the autistic girl. Both Hendel and Gillian were picked by the captain of the Idenna to accompany him on his search for a new quarian homeworld.
Mass Effect: Deception
Note: This section features material from the first edition of Mass Effect: Deception, which BioWare has acknowledged contains discrepancies with other Mass Effect lore. Once revised editions of the book are released, this section will be updated.
After her escape from Cerberus, Gillian has become a trusted member of the Idenna's crew and has earned the quarian name "Gillian nar Idenna". She serves on the Idenna's security force with her mentor, Hendel Mitra. When the Idenna comes under attack from the Glory of Khar'shan, a batarian slave ship, Gillian's advanced biotic abilities turn the tables on the slavers and allow the quarians to capture their ship. One of the slaves aboard the ship is Hal McCann, a Cerberus operative who knew Gillian's father, Paul Grayson. After learning of her father's death from McCann, Gillian resolves to find her father's killer and exact vengeance. Knowing that the Idenna's crew won't refuse her after she had saved them from the batarians, she asks for and receives the Glory of Khar'shan to fly to the Citadel.
- When Kahlee asks Gillian what she knows about the quarians, Gillian begins quoting verbatim from her history book. This quotation is actually the beginning of the quarians' primary Codex entry in Mass Effect.
- In Mass Effect: Deception, Gillian's age is given as 18 and it is stated that six years have passed since she met Hendel Mitra at age 12 in Mass Effect: Ascension. This conflicts with Deception's place in the overall Mass Effect timeline. Ascension occurred in 2183 CE and Deception occurs prior to Mass Effect 3 in 2186 CE, so only three years could have passed; Gillian should be no older than 15 in Deception.