Think of it as the average hentai, with the Kwantung Army playing the part of the schoolgirl and the Red Army as the tentacle monster, forcing its way into every orifice the Kwantung Army has and a few it didn't have until the Soviets went to work.
^ Yep, that would be about the reality.
The Japanese would probably see that and get the heck back to Korea before Stalin's forces showed up.