Cornelia (often referred to as Corey for short) is Artemis and Chiaro's younger sister.  From childhood, Cornelia and her younger twin sister Caroline were near-inseparable, but started to grow apart in their teenage years. Corey was always the more reclusive, introverted twin; Carol was the one that craved individuality and went out of her way to make new friends and strive for popularity. This left Cornelia feeling abandoned by the one person that was supposed to be closest to her, and she eventually developed mental instabilities down the line. While Caroline's interests were geared towards trends, fashion, and friends, Cornelia had a penchant for horror films and the occult. She was taken to many therapists when her behavior began to show unsettling tendencies, but she dislikes taking the medication prescribed for her. Like Artemis, Cornelia inherited her supernatural powers from their father, while Caroline was born without any such phenomena from either parent. Cornelia currently shares an apartment with Artemis, who keeps her state of mind in check.

When voicing her, note that Cornelia can be relatively moody. Her normal speaking voice can sound withdrawn and shy, but she is more than capable of dialing it up to express anger or excitement.