This looks like an unreliable narrative style. All the flashbacks are only shown from Mizuki's perspective, so they are not necessarily true. Could be all lies.
So basically this is Breaking Bad: Manchukuo edition.
As expected of japanese propaganda, they still try to portray the jap as "not that bad" and the chinese/manchu as "not that oppressed".
Some of the chinese names are bastardized into japanese. Please don't translate like that, it becomes...
The doctor's identity is one of the biggest unsolved mystery and the chapter leaves us with cliffhanger.
Does the idaten even age? Rin's predecessors were all grandpas.