Joker Game is set from 1937 and later. During this time, Japan was in its Imperial Era, where every male was required to serve in the Imperial Army. Many women were forced into gender roles that would not allow them to become soldiers in the war. You can read more about Japanese women's role in WWII here.
However, D-Agency is definitely under different ...
the chronological order of the episodes goes as follows:
D Agency founded in autumn 1937
Episodes 1 & 2 ("Joker Game Part 1 & 2") - Spring 1939
Episode 12 ("XX - Double Cross") - Spring 1939
Episode 6 ("Asia Express") - July 25, ...
I believe it's the Imperial General Staff Headquarters. (Photo from Geospatial Information Authority of Japan for comparison below. Similar images in the postcards scanned in the link.)
As for the statue it seems to be of the founder of the General Chief of Staff, Prince Arisugawa Taruhito. While the current statue is now currently located in Arisugawa ...