Cathrine Deboucoillet attends St. Luminous Mission High School as a member of its art class. Maintaining a reclusive disposition, she expresses herself through painting on school building walls, using this as her primary method of engaging with her surroundings. She lives in room 711 of the women's dormitory. During school events, Cathrine directly witnessed the disappearance of fellow student Asako Sato from the pool area, positioning her within the incidents affecting students. She has red hair cut to neck length and blue eyes.