During the Second Sino-Japanese War in 1938, assigned to the 12th Air Group, Kuroiwa saw considerable action against Chinese air opponents. During his combat career, Kuroiwa was officially credited with shooting down 13 enemy aircraft. In 1939 he was deemed too old to continue with combat duty so Kuroiwa left the IJN and became a civilian pilot for Imperial Japanese Airways. On 26 August 1944 the civilian transport aircraft he was flying disappeared off the Malay Peninsula and neither the aircraft nor Kuroiwa was ever found.