Date of birth: c. 1978
Gender: Female
Height: 163 cm (5 ft 4 in)
Mass: 58 kg (128 lb)
Race/Ethnicity: Japanese/American
Occupation: University Student
Former Umbrella Corporation employee

Born in the United States, Yoko learned to speak Japanese through her mother. At some point, Yoko joined Umbrella as an employee of Dr. William Birkin, working in his Laboratory eight miles outside of Raccoon City.

In 1996, Yoko took part in an experiment to test the effects of the t-Virus, and, after a "little incident", she fled. The memories of what occurred were so traumatic that her mind hid them from her to protect her.