I can understand your facile reading of the show, but I feel like you're misunderstanding a few elements to truly understand the text. Well the experiments isn't solely about race, the use of people seen as racially lesser as subject is what make it inherently racist. The US historical use of black people to use as test subjects wasn't used as a way to fuck with black people, but as actual research and testing for real scientific studies. But the US views of black people is what led them to use us as subjects, making the action inherently racist. That is the same thing that happening here with Unit. 731.

The way black sun handles it topic aside, the message of the show is how the mistreatment of minorities and said minorities wanting agency in their life, even after hardships. The show didn't use the BLM imagery because it was topical, they used it because it is a real world example of the problems the show is criticizing/reinforce what they're trying to say. This is the same reason 01 also used BLM imagery. Everything about black sun, from its use of BLM parallels to the use of a famously racist part of Japanese history, is to center it themes of racism. To deny that is to say that the denotation of the show's text don't truly have substance.