Emi Nishimura's identity quest began the hard way.
A 39-year-old mother of three children, Nishimura felt pressured to take care of her aging father when her parents got divorced seven years ago. But then one day when she was telling her mother how unfair the situation felt to her, she was given an explanation she had never expected.
"My mother told me I didn't have to worry about him, because he wasn't my biological father," the petite, soft-spoken woman said in a recent interview. Then her mother told her, Nishimura recalled, that she used to make frequent trips all the way from their hometown in western Japan to a Tokyo hospital to undergo an infertility treatment, and eventually became pregnant — through the sperm of an anonymous donor.