Imperial Japan very much did test bio weapons on civilians
They’re both no longer a superpower as well as being a client state of the US now.
Additional fun fact: the USSR was the only country to put Unit 731 war criminals on trial (although they only caught a few of them), a move which the USA denounced (going so far as to ban the distribution of the trial transcripts). Less fun is that they all received fairly mild sentences with the longest being 20 years, but none of them served more than 7 before Khrushchev had all of the ones still in prison repatriated to Japan.