Invisible. Japan had eyes and ears through asia and would've seen a noteworthy advance of infantry. They could contest in china, in the infantries crossing of the sea, and maybe even defend a beachhead.
The 30 million+ russian riflemen could not teleport. It was extremely important that they widdle at the forces in stalingrad, or else the Germans would have seized a majority of russia. In addition, the Russians would have had to cross over china without the help of trains via lend lease while china had been invaded by japan, was suffering from a famine, and was being bombed by japan.
Japan also may have also delayed pearl harbor, which actually would have been bad for japan because the U.S. was basically already on the side of the allies before the war started by landing sanctions on japan and selling goods to britain.
It may result in Russian victory but it would be ugly and actually more than likely result in defeat because the Russians barely where able to feed and arm their 30 million riflemen, let alone have them simultaneously cross an ocean in ships under the fire of the Japanese navy and air force.