How would the Keions react if they knew about Unit 731 (google it if you don't know what that is).
About the same as any other Japanese youth would feel about it. They don't know about it, and if informed would regard it the same way that they don't care about Hiroshima & Nagasaki.
Were you expecting suffering?
Admit it, you don't actually want to talk keion. You want to get history in /a/.
They would react the same way they react to everything else: cutely.
How would Murrikans react if they knew that Unit 731 was pardoned by Murrikans in exchange for their research?
Mugi and Mio already know. Mugi just regards it as one of the many facts she knows. Mio lies awake at night imagining the horror.