Karen was the Student Council Secretary and a participant in The Tragedy of Hope's Peak Academy. She was the one who started the Student Council Killing Game after she read the motive that Junko Enoshima presented to her.
Karen has short brownish green hair, which falls just above her shoulders and is slightly curled; notably, two of her bangs cross over each other on either side of her eyes. She has blue-green eyes behind her thin white glasses, and she wears the standard uniform of Hope's Peak Academy.
Karen cared for her mother deeply while being somewhat weak-willed or easily manipulated, as she was driven to start the Student Council Killing Game after she found out something bad happened to her mother.
She loses her sanity during the killing game and she, unlike most of the other students, appears to turn very sadistic while murdering others.
Karen was one of the student council members called by Junko to participate in her new killing game. Karen was initially as reluctant as any of the council members, but she became the first to fall victim to Junko's "motivation"; when she looked in her file, she found a photograph showing something horrible happening to her mother.
Overcome with fear, Karen seized a katana and quickly impaled Ryōta, becoming the first student council member to kill. Crying incoherently about her mother's fates, she furiously tried to attack Sōshun Murasame, only to miss and get her katana lodged in a desk.
Karen later appeared in the hallways, covered in blood and wielding a chainsaw. She smiled evilly at Sōsuke, who was breaking down over the bodies of his latest victims before presumably murdering him in turn. She eventually returned to the classroom where the carnage began, where she was killed by one of the other survivors - possibly Asukasei, as he was seen holding her chainsaw after becoming the apparent sole survivor of the killing game.
Although never actually shown with her mother, Karen loves her mother more than anything and is very close to her. When shown evidence that her mother was dead, she started the Killing Game without hesitation and subsequently fell into despair.
Although Karen was close with her fellow Student Council members, she immediately started the killing game after being told of her mother's demise, showing no regret and even seen smiling as she murdered her friends.
- Her given name, "Karen" (かれん) written in Kanji (華蓮) could translate to "splendor flower."
- Her last name "Kisaragi" (如月) means the second month of the lunar calendar.