Katiana O'Sullivan, also known as 'Kat' and born 'Kathy O'Sullivan' is a 16 year old supernatural who first appears in the Darkest Powers/Darkness Rising short story Kat and then later in the short story Hunting Kat. It is unknown if she uses O'Sullivan as her surname, only that it was the one she was born with. She is a subject of The Edison Group's Genesis II Project, with of two known hereditary Vampires included in the project and the ward of the Vampire Marguerite.
Kat describes herself as having sleek golden brown hair, tanned skin and tilted green eyes. Marguerite often calls her by the nickname mon chaton which is French for my kitten and also related to the fact that she's a good climber and they'd joked about Kat being a werecat. Kat doesn't like mysteries and things she can't see to fight, such as spells. She wore a Star of David given to her by Marguerite, she believed it was part of their cover but it was so if Kat died her body wouldn't be embalmed. Before she became a Vampire, Kat dreamed of a career in sports medicine and had spent her summers volunteering at a clinic.
When she was little, Kat lived with her mother and father who had named her Kathy. Her parents had seemed more like guardians but there was no affection in their home. Once a month, she was woken in the middle of the night and taken to a "hospital" where Dr. Marcel Davidoff would run several tests on her. Her parents told her she needed these tests because she was sick, they would leave her weak and sore for days.
When she was in kindergarden, Kat met Marguerite for the first time when Marguerite became the library assistant at her. Marguerite would come over and talked to her whenever she was alone and stayed with her when she waited to be picked up, she was kind and affectionate towards Kat and was loved by all the children. One day, Marguerite said that she had to leave and asked Kat to come with her. Kat agreed.
They went to live in Montreal where Kat chose her new name and Marguerite acted as her aunt. A few years after Kat had been living with her, Marguerite told her the truth about the supernatural world and that she was a genetic experiment. Marguerite had been part of the group monitoring the supernaturals but she couldn't sit by and just watch Kat be miserable so she took her against her groups orders. In the short story Kat is unbothered by watching Marguerite feed, she believes it's just simple eating and that anything more is overcomplicating something simple.
In Kat: Edit
Kat is now 16 and is woken up by Marguerite who informs her that Vampire hunters have found them. They then escape their current house/hideout and get onto the streets.
Kat notices that Marguerite need to feed before they go down an alley. There, she spots a homeless man and tells Marguerite to feed. After Marguerite fed she slipped the unconscious homeless man money before they went to the nearby bus station.
While at the bus station, she saw a woman approach her, calling out her birth name. Marguerite then tells her that they will call a taxi but two men approach them and they have to run. They ran until they were trapped in an alley.
After a short battle where Marguerite is shot, they saw a city bus and flagged it down. She learns that the men chasing them were not Vampire hunters, that they were in fact from the Edison Group. They continue running until Kat is shot in the heart by one of The Edison Group in trying to trade herself for Marguerite's freedom after she was captured.
She was shot by an Edison Group member who doesn't think Dr. Davidoff will complain as he can test his theory about Kat. She later wakes in the morgue as a Vampire.
In Hunting Kat: Edit
Kat is forced off the road by bounty hunters six months after the events of the short story Kat. She meets two other captives of the men, Neil Waller and Chad. Chad turns out to be a Half Demon relative of the bounty hunters as well as a likely Edison Group subject himself.
Kat escapes with Neil whose parents believed the Edison Group's experiments would ensure he wouldn't be reborn after death. Kat is reunited with Marguerite and stops struggling with the shame and fear of feeding on humans. Together with Neil and his parents they agree to attend a Vampire meeting in New York to try and discover more about what the genetic manipulations have done to them. It is also hinted that she and Neil will later become romantically involved.
In the short story Kat, she mentions that her skills come from the training she had done. She is a competition-level gymnast, a brown belt in karate, and a second-degree black belt in aikido. Before being reborn as a Vampire the only ability she showed in her human life was some minor enhanced night vision.
After Kat becomes a Vampire, Margueritte tells her that The Edison Group's modifications are supposed to allow her to grow and age as normal while retaining the other powers of a Vampire. She doesn't need to eat and drink but unlike other Vampires she can do it as normal without risking upsetting her stomach. As of the events of Hunting Kat she still unsure whether or not she is ageing.