Who says the Northeastern Army never fought the Japanese? The 67th Army, pushed aside by the Generalissimo, was sent to the Battle of Shanghai. Only 130 men remained. They endured countless hardships, fighting north to reclaim their homeland, only to be swallowed up by their own allied forces in the end.
Then I'll fulfill their unfulfilled wish: fight our way home and wage the war of resistance amid the mountains and rivers of the Northeast.