"A mysterious young woman, Yoko claims to be a twenty year old student of Raccoon City's prestigious local university. An expert with computers, she is a somewhat shy and soft-spoken person, although she is prone to bouts of uncharacteristic bravery when it is needed the most. She has a highly inquisitive mind and once focused on something, she will relentlessly pursue her goal until it is achieved. In her spare time, she collects various kinds of gadgetry and is a voracious reader.
Yoko was originally employed, presumably as a computer technician, in William Birkin's laboratory underneath Raccoon City. She was also one of the subjects who donated cells to the project that would create the Tyrant. Subsequently, Yoko was operated upon by an Umbrella researcher named Greg Mueller, to suppress her memories of the experiment. In her best ending for File #2, Yoko regains her memory as she watches the destruction of Raccoon City, and goes on to testify against Umbrella in court." fr. wikipedia.