Karen serves as a Berühren Corporation operative stationed at an orphanage functioning as a front for unethical experiments involving child subjects and cybernetic Extensions. Her primary mission involves retrieving escaped subjects, specifically Tetsuro Arahabaki, who possesses an illegal remote-control device, Harmony, implanted in his medulla oblongata.

She uses deception during operations, such as posing as a nun to approach Juzo Inui and secure custody of Tetsuro. When her ruse fails, she reveals her Berühren affiliation and initiates combat. Her cybernetic enhancement includes a specialized right eye that enhances her marksmanship, enabling precise ricochet shots targeting weak points in opponents' Extensions, like auxiliary sub-brains.

During a sewer confrontation, Karen shoots both Juzo and the Extended body controlled by Tetsuro, inflicting critical injuries. She successfully recaptures Tetsuro and transports him via train to a Berühren facility. However, Juzo intercepts the train by derailing it, incapacitates Karen, and rescues Tetsuro.