I've traveled to both countries, while in my experience the Chinese weren't overly hostile to me, I could say they were generally less than friendly. Like very curt.
Japanese people are very much about politeness, so they will generally treat you ok even if hey don't care for you. There is some ignorance to Black culture among older people but the younger kids (under 35) are kind of reverent of it. Especially hip-hop. Like that's their counter culture music. They are very big on stuff like Jazz and even funk. They also have a thing especially about Black masculinity, like the men are intimidated and the women are curious especially since their own men are leaving them high and dry.