Bourne Thunder: 1937

In Shanghai in 1937, the protagonist lurks as a trading company manager, but actually masters the Japanese military's top password system. He established a "ghost intelligence network" to transform deciphered intelligence into precise beheading operations. Every successful decipherment corresponds to the mysterious death of a high-ranking Japanese military officer. The Japanese army became suspicious and launched a bloody purge, while the protagonist watched the enemies kill each other in the dark.