Explanation: Unit 731 was a grotesque 'research' unit of the Japanese Empire in WW2, whose experiments were... incredibly brutal, unethical, and illegal by international law, murdering tens or even hundreds of thousands of Chinese civilians in the process. Don't look up example descriptions of their experiments unless you have a strong stomach.

After WW2, MacArthur, the American general in charge of occupying surrendered Japan, ended up offering the doctors of Unit 731 immunity in exchange for their cooperation in recovering the data of their experiments. The thinking being that SURELY Japan, in causing so many deaths and investing so many resources into a research division during a time of desperate and total war, must have some incredible results from their wartime super-science program to justify its existence!

... turns out, no, not only were most of the experiments fucking worthless, but the remainder that had any hypothesis with actual medical relevance were often done with shoddy methodology and record-keeping; and the one or two that may have had a greater-than-zero level of research professionalism have been largely rejected by the post-war scientific community for ethical concerns of using data extracted from a fucking torture unit.

So good going. Immunity in exchange for fuck-all.