Shadows of Espionage: The Republic-Era King of Secret Agents

Entirely fictional. I hope you enjoy it. (Many items from outside the era appear in this story.)

In a Republic-era espionage world during the War of Resistance Against Japan, someone transmigrates into the body of a lieutenant in the Military Statistics Bureau, while also serving as an undercover agent for the Communist Party. Pressured by the Japanese army, the Military Statistics Bureau, and the Central Bureau of Investigation, every mission is fraught with danger. By chance, he obtains the “Spy Insight System,” which can uncover intelligence, exchange for skills, and predict the state of affairs. The System lets him thrive among the various factions and quickly distinguish himself, far surpassing his peers. With its help, he rises through the ranks, builds his own force, and ultimately foils the enemy's schemes. He becomes a legendary double agent who helps preserve the peace after the war, then retires in glory.