The Student Council Secretary of Hope's Peak Academy.

Spoiler

She and the rest of the council were forced into a killing game by Junko Enoshima and Mukuro Ikusaba, an event that would later become known as the The Tragedy of Hope's Peak Academy. Karen was the one who started the Student Council Killing Game after she saw the motive that Junko Enoshima presented to her, a photograph of something horrible happening to her mother. Overcome with fear, Karen seized a katana and impaled Ryouta, becoming the first student council member to kill.