Karen is a mature tall beauty. She has short curly red hair with bangs styled to the right. Karen often wears revealing clothing.
A devout catholic, Karen was abused by her fundamentalist mother when her power to manipulate fire manifested in her childhood. After her mother died, she was, according to the anime TV series, raised by a kindly priest, but she continued to remember her mother's last words: "No one would be sad if you died!" In the CD dramas it is shown that Karen was scouted by several religious sects in her childhood, but her mother would always shoo them away, saying her daughter was a demon and not a messiah. Her barrier field is shaped like a cruciform prism.
As an adult, Karen works as a call girl for the soapland brothel "Flower," and often enters battle wearing her "work clothes," though she retains some of her childhood innocence in her beloved teddy bear, Paul. Aoki visits her at work for an interview, but, like a gentleman, refuses to take advantage of her; she comes to admire him for this. It is suggested that Karen feels a strong affection—and probably a romantic attraction—for Aoki, but she has refrained from telling Aoki as much, likely out of respect for him and for his family.
Karen sacrifices her life to kill Yūto in order to protect Aoki.
Karen and Shōgo battle in the subway. Karen causes a massive explosion, causing them both to be crushed by debris.
Karen is a flame master and arguably the most powerful woman in the X's universe, especially in terms of raw power, skills and fighting abilities. Karen can summon her own kekkai that's shaped like a cross.
In Other Media
Karen appears twice in Tsubasa as a crossover character: in the world of Shara-no, she's the leading woman in an entertainment troupe and in the world of Tokyo, one of the seven fighters of the Tower faction. In the X Tarot set, she represents Justice.