The Polish and Japanese had a surprisingly friendly interwar relationship in part due to their mutual animosity against the Soviet Union. In the wake of the Russian Civil War, a large scale Entente coalition force was occupying the Russian Far East in what was known as the Siberian Intervention. Though most of the Entente pulled out of Russia by 1920, the Japanese retained a substantial military presence in the area as they were concerned about a Soviet incursion into Japanese Korea as well as Japanese-influenced Manchuria.

The chaos of the Civil War had created a major humanitarian situation where refugees from all over the former Russian Empire had fled to Siberia in hopes of safety. Among their number was a large number of Poles, a mix of anti-Russian and anti-communist freedom fighters as well as civilians. Several Poles in Vladivostok requested that the Japanese government take in Polish orphans from Siberia as a humanitarian initiative. Japan at this time was still fairly pro-Western, and so they chose to accept the task as part of a diplomatic effort to impress the West. Over 700 orphans were successfully evacuated to the port of Tsuruga in Japan, after which they made their way through the Americas into Europe and safely back into newly liberated Poland.

As many of these orphans grew up, a number of them became senior government and military officials in the Polish Republic. They retained a sense of goodwill from the Japanese government, and the Japanese government in turn saw Poland as a useful ally against not only the Soviet Union but also against Nazi Germany. For the Japanese, the Polish intelligence service was one of their most important sources of information-gathering in Europe. This especially became an issue in the wake of the Molotov-Ribbentrop Pact, which Japan saw as a major betrayal by the Germans. Japan had allied with Germany in the Anti-Comintern pact, aimed against the Soviet Union, and this sudden apparent German-Soviet alliance severely antagonized the Japanese government who saw parallels with the collapse of the Anglo-Japanese alliance in the 1920s. The Japanese at this point stepped up their intelligence cooperation with Poland against both Germany and the Soviets, and even though the Polish government-in-exile declared war on Japan in 1941 the Japanese more or less ignored the declaration of war and continued to coordinate with the Poles against the Soviet Union. The Poles, for their part, were more than happy to supply information on Germany and the Soviets to the Japanese. In turn, the Japanese issued diplomatic papers and passports to Polish agents that allowed them to travel in Axis territory, and the Japanese embassies and consulates facilitated Polish espionage efforts on numerous occasions. Chiune Sugihara, the Japanese consul to Lithuania now known for his work in saving thousands of Jews from the Holocaust, had a translator on his diplomatic staff that was actually a Polish officer. The mutual espionage between Poland and Japan was significant enough to cause Stalin concerns about a joint Polish-Japanese attack on the Soviet Union in the 1930s, and may have been a contributing factor to his Great Purge, which allegedly targeted Polish and Japanese spies in particular as well as German ones.