Unite D III: Paradise Lost by Koji Yanahgi is a decent continuity of his Unite D series, which star a bunch of Japanese spies and their mysterious leader who is only known as Demon King.
Like the prequels before it, the four short stories within Paradise Lost take place during WWII, the war among different spies are still satisfyingly written and entertaining although as a Chinese whose country had once suffered eight long years of bloody battles with the Japanese imperial army during *both* Sino-Japanese War and WWII, unsurprisingly I don't find some of the spies' justification for their missions and action endearing.
But don't worry, it's not a propaganda for Imperialism (the Demon King forbade his spies to kill people or seek a glorified death for themselves and he even thought an all-out war is a stupid idea) the author focuses more on the 'game of wit' aspect of the spies' activities and the internal struggle of reason, loyalty and emotion the spies have gone through when they tried to accomplice their missions.