She was born in Osaka, Japan (from where she took her surname) to a Japanese mother and a Haitian father. It's true she has lived most of her life in the US but she chose to represent her country of birth when in her early teens with her family's encouragement. She is not yet fully fluent in Japanese but she is learning the language. To me, her accent already sounds a bit Japanese. Mary Pierce was born in Canada, grew up in the US, but chose to represent her mother's country, France. Maria Sharapova grew up and still lives in the US but has always chosen to represent Russia, her country of birth. Such examples are not uncommon.