Catherine arrives mysteriously as a transfer student midway through the series, joining Licca Kayama's school. Initially perceived as a stoic and aloof figure whose unusual behavior marks her as a potential Creepy Child, this impression later shifts when her true purpose emerges. She is revealed as a soldier from the Doll Kingdom, fiercely dedicated to protecting Princess Licca.

Acting as an Anonymous Benefactor, Catherine secretly aids Licca during crises. Her primary tool is the "Calling Choker" or "Calling Ring," entrusted to her by Franz, a former Doll Kingdom resident now in hiding. Using the incantation "Fururu Furora Gurine Guraine," she anonymously summons the second Doll Knight, Izumi, to Licca's defense.

Her Undying Loyalty drives her actions within the royal family's conflict, guided by Franz. Her mission takes a perilous turn when she is kidnapped by Misty, a bat-devil minion of the demon Devaul. During this abduction, she loses her vital Calling Choker, which is later found by Licca's friend, Sumire Shinohara, who becomes Izumi's new summoner. This capture reveals her vulnerability, positioning her as a Badass in Distress.

Following her rescue, Catherine evolves from an Aloof Ally into an integrated member of Licca's protective circle. She remains actively involved in thwarting Devaul and safeguarding the Doll Kingdom's legacy in the human world.

Catherine possesses a youthful appearance with blue hair styled to shoulder length, gray eyes, and typically wears a school uniform, tie, and hair ribbons. This schoolgirl look contrasts with her determined and courageous demeanor, embodying the essence of a Little Miss Badass fulfilling a critical mission.