Changsha is the capital of Hunan, which is a central southern province of China. This drama is set in 1939 at the prelude to the first Battle of Changsha and it was also the beginning of WW2. There were actually 4 bloody battles in total from 1939 to 1934, where the Japanese tried and failed to take the city. It is significant because this prevented the Japanese from consolidating their territories in Southern China. It was one of the important achievements the Nationalist Army of Chiang Kai-shek's Republic of China. The CPC, which was founded in 1921, did not come into power in China until 1949. Xue Yue (who is on the cast list) is a real historical figure and the commander of Changsha's defense at the time.
The rest is plot speculation and there will be spoilers:
During this time, the Japanese already controlled Shanghai via their collaboration with the Wang Puppet Regime but in Changsha, the KMT is still firmly in charge and while the Japanese may have moles in lower or even mid-level positions, they should not be in direct control of the NBIS or Changsha's military defense operations. If they were in control of Changsha already, they don't need to try to invade it. If they have high placed agents in NBIS or among the military, Kunwu wouldn't have needed to get Qu to steal the defense map. So Kunwu is more likely to be someone hiding among the mid to lower ranks of the NBIS Hunan Station or the military defense operations.
We can assume that the CPC's role in this narrative will be to "save the day" behind the scenes by helping to weed out the hidden Japanese moles within the KMT. This puts both Yang Jiming and Assistant Wu in the good guy camp. They are all hidden CPC spies. At the time CPC were the underground rebels or freedom fighters depending on your point of view, so anyone being part of their organization kept it a huge secret.
Muzhi's secret is simply that he is also a hidden member of the CPC and he was grooming Hongshen to join the CPC as well. Most likely his father before him was also a CPC member.
Kunwu's painting was for Xu Meijia to send back to Japan. It is a message to his 3 family members that he will soon reunite with them. That suggests they are not in Changsha with him. Its just a red herring, no need to try to overthink who they are. The other possibility is that the sketch is a threat with the sword pointing towards someone's family that is being held hostage in Japan.
Chiang Kai-shek initially considered giving up Changsha around 1938 but reconsidered due to its strategic importance. This explains Deputy Chief Zhu's excuse of helping wealthy members of the Changsha community to move assets out of Changsha. It is suggested that Zhu is somehow related to the Commander, which I assume has to be Chiang. Thus Ke JP's reluctance to prosecute him is understandable.
The Japanese favored battle tactic is a direct assault on the front followed by surprise attacks from the flank to breakthrough their enemy's defenses. However, Hunan's terrain is complex so in order to flank Changsha, the Japanese army can only march from the east or the west. Changsha's resources are limited so they are unable to defend both sides. So it is important that they understand whether the Japanese will come from the West Yueyang Lake or from the East from the direction of Jiangxi. This is according to Yang Ziming in Ep 7. In history, in the first battle of Changsha, the Japanese ended up marching from the East/Jiangxi. When Hongshen decodes the intelligence, we will see whether that is the attack plan.
We now know Kunwu is a man.
The Director has confirmed that Kunwu appeared in the first 8 episodes of the drama. He graduated from the Whampoa Military Academy and joined the National Army in 1925 suggesting he is between 32 and 39 years old. This rules out both Yun brothers and likely Ling Han as well.
I will update as appropriate as we go along:
First update: Nov 21, 2024.