Her parents died while she was still in high school the exact details are unknown. After that, she somehow met Cleo Dahmer and became her intern at the facility. She would then spend the next several years working closely with Dahmer in her experiments on the Left Hands, and eventually reach her own degree of renown amongst the facility's staff.
Circe has a very cynical outlook of the world and people. Much like her mentor Dahmer, Circe chooses to view the world as a scientist first and foremost. She goes to great lengths in order to keep her every action as efficient as possible and refuses to interact with anyone she deems as being a detriment to her efficiency. She only sleeps for about three hours, she eats raw meat, and every waking moment is dedicated to her work.
She comes off as very cold and distant to others, and doesn't emote very much at all except for the mild annoyance of having to work with people she considers to be hindrances. At the very least she is not heartless. She admits to having difficulty communicating with others general and claims to have a "small" god complex.
In the original timeline of Design, where John is taken to the facility and made into a Left Hand Circe is encountered as the class 8 god bearer unit Subject 888. She appears to be much happier as a god bearer, but this is revealed to be a forced persona. She claims to have felt no remorse for her treatment of the god bearer test subjects when she worked under Dahmer, having justified the experiments in her own mind by saying they were making progress towards a safer future for humanity. Unfortunately, after becoming a test subject herself, she was made to realize the full weight and cruelty of what she had been doing. Her attempts to come as cheery and sociable are both her way of coping with the trauma of how her life has unfolded, and simultaneously a way of trying to raise the other test subjects spirits.
She appears as a loud, cheery individual when she is first introduced. She is usually uncaring of those around her and will often be cruel when she feels irritated. She continues to mostly hold this appearance for the majority of C-2 but she does reveal that she can be hurt. When she is not doing anything of importance she will often be doing something like a impersonating a classroom of people suggesting she has some multiple personality issues.
Circe is incredibly intelligent. She is able to analyze and take into account all of the details regarding any given situation and put them together to make a solution with very little effort. Within hours of Subject 12's escape, she was able to figure out where the Left Hand was most likely to go, what course of action it was most likely to take, and tracked down John Matthews who was most likely to be able to access the data currently unavailable to the facility. Even when forced to improvise, she is able to come up with surprisingly complicated schemes. She was able to kill a Left Hand using nothing but a knife and one soldier as a sacrifice.
As an 8 class god bearer unit, Circe's ability to conduct matter distortion is considered to be below average. That being said she is still capable of telekinetically lifting and moving objects or tearing people apart with relative ease.
Circe has four wire chords embedded within her back which can be controlled like limbs through matter distortion.
Through matter distortion, she is capable of reconstructing her body one particle at a time, should she ever sustain non lethal damage.
Circe appears to somehow shift her consciousness between the Homebound and Facility timelines at unknown intervals. How, why, and how often are all unknown.
She was able to reattach her head after it was sliced clean off by Ell's scythe and recover the damage done to her by other C-2 creatures and being slashed.
One of her new abilities after 'dying'. She is able to use them with what are remains of her rib cage and tear apart other C-2 creatures.
She is unable to feel any sort of pain as shown when she is slashed by Salem and when her arms get torn off.
- Her flesh may be able to regenerate in C-2 strain but it also has been weakened as shown when her arms tore from their sockets when she tried to catch Ell.
- She always seems to be thinking similarly to a narrator with the exception of her Facility arc incarnation, stating what she is doing and such.