In 1934, Kaji was charged with violating the Peace Preservation Law and threatening the Kokutai, being jailed for around a year and resulting in his flight to China in January 1936.

[5] While in China, Kaji met Lu Xun,[6][7] Hu Feng,[8] Xiao Hong,[9] Edgar Snow,[10] and Koji Ariyoshi.

[12] In Shanghai, Kaji was placed under suspicion for working with Japanese socialists by Chiang Kai-shek's Nationalist government,[13] fleeing following the start of the Second Sino-Japanese War to Hankou via Hong Kong, then to Chongqing.

[5] During the war, in December 1939, Kaji founded the Japanese People's Anti-war Alliance,[14] which was disbanded the following year due to a breakdown in relations between the Kuomintang and Communist Party and a subsequent increase in suspicion of leftists by the Nationalists.

In response, the OSS said it would "make no guarantees" but "would not hinder" his larger work with his group, the League for the Establishment of a Democratic Japan, an offshoot of the Japanese People's Anti-war Alliance that sought "the ultimate liberation of Japanese society from authoritarian political oppression and ... industrial capitalist exploitation" so long as the work's sponsorship was not traceable back to the OSS.

[4] On 25 November 1951, Kaji was kidnapped by the Z-Unit (a black operations under Lt. Col Jack Canon), in what is today the city of Fujisawa, Kanagawa, and was held for more than a year in several locations.

[4] U.S. sources at the time, including the Embassy of the United States in Tokyo, disputed this account, with a statement issued on 15 December saying Kaji admitted to being "an active Communist intelligence agent" after his capture, and that he had concocted the story of being kidnapped due to a possible threat against his life from his superiors.

Details later emerged that Kaji was under surveillance by the U.S. prior to the other man becoming a double agent for the CIC, meaning that intelligence from him could not have been evidence proving the U.S. claim.

[18] Wataru Kaji was featured in the International Friends During the Anti-Japanese War, an exhibition organized by the Beijing People's Association for Friendship with Foreign Countries.