In 1937, before World War II begins in earnest. Lieutenant Colonel Yūki of the Imperial Japanese Army forms the "D Agency," an army intelligence outfit under his command and tutelage. Army General Staff attaches Lieutenant Sakuma to observe the unit's performance. D Agency casts a wide net to find agents beyond Japanese military personnel, and Yūki establishes D Agency's tenets, which go against IJA doctrine: "Don't kill, don't get killed, don't get captured." With this, Yūki trains a team of operatives who conduct missions against domestic and foreign powers.