What race is a child if he has Japanese father and Black mother?

It's important to understand that race is a social construct, not a biological one. There is no scientifically valid way to determine a person's "race" based on their parents' racial backgrounds.

A child with a Japanese father and Black mother will likely identify as biracial, multiracial, or simply mixed race. The child may choose to identify more strongly with one heritage than the other, or they may embrace both equally.

Ultimately, how the child identifies racially is up to them, and it may change over time. It's crucial to respect their self-identification and avoid making assumptions based on their parentage.