There was an "army" called "Northeast Anti Japanese United Army" ( English Wiki ) organized under the main control of the Communist Party Of China ( the name then ).
But as you can read at the link,
At the peak of their activities, NAJUA had a force of 10,000 troops. They launched the guerrilla warfare in the rear of Japanese army, who was invading the main land China. Japanese army realized that NAJUA was the main threat to their operation in the mainland China. So Japanese army, together with Manchukuo army, began the operations to sweep NAJUA in mid-1930. Like NAJUA, Manchkuo army included many Korean officers who pledged their loyalty to Japan. Such Korean officers were Park Chung-Hee, Baek Seon Yeop, and Jeong Il-Gwon, who later became the full generals in South Korean Army and (after May 16 coup) high rank officials in South Korean government. And Manchkuo army had a special troop, Jiandao Teshedui (Chinese: 間島特設隊, Korean: 간도특설대), which consisted mainly of Koreans. They assumed the most difficult tasks to attack NAJUA.
As the offensive of Japanese army got fierce, NAJUA suffered heavy casualties. Many of their soldiers were dead or taken prisoner. Moreover, Japanese military intelligence allured or tortured NAJUA prisoners to convert to Japanese side. The converted one assisted Japanese to attack their ex-comrades. In his autobiography, Segiwa Deobuleo (세기와 더불어), Kim Il-Sung recalled that such conversions of ex-comrades were more painful than Japanese fierce offensive or tough climate in Manchuria. By these reasons, NAJUA could not make activities in Manchuria any more. By the order of CPC, NAJUA escaped to the USSR. There, they were formally incorporated to the Red Army, as the 88th International Brigade, but they kept the organization of NAJUA. The troops remaining in Manchuria were totally annihilated by Japanese. The escaped troops stayed in USSR until the war ended. After Japan surrendered, Koreans and Chinese went back to their own countries and began the revolutionary activities there.
So unfortunately there was no group called an "army" even the size of the "organized group" as of 1944 largely active in anti Japanese activities. It was until the USSR invaded Manchuria that the "anti-Japanese" activities started to "function".