With World War II right around the corner, intelligence on other countries' social and economic situation has become a valuable asset. As a result, Japan has established a new spy organization known as the "D Agency" to obtain this weapon. Under the command of Lieutenant Colonel Yuuki, eight agents have been assigned to infiltrate and observe some of the most powerful countries, reporting on any developments associated with the war. In order to carry out these dangerous tasks, these men have trained their bodies to survive in extreme conditions and studied numerous fields such as communications and languages. However, their greatest strength lies in their ability to manipulate people in order to obtain the information necessary to give their nation the upper hand. Taking place in the year 1937 on the eve of World War II, the story involves a mysterious spy training organization known as the "D Agency." The organization is established by Lieutenant Colonel Yuuki from the Imperial Japanese Army. His ideals lead him to recruit people beyond military academy graduates and personnel, while training them to become skilled agents in arts of manipulation. These agents would become a specialized team to conduct operations. One such antihero agent, under the name Jirou Gamou, goes on a harrowing mission to uncover secret documents titled "Black Notes," while battling forces from within and without his own ranks.