Japan actually had a superior atomic bomb research program than the German's during WWII. They had both the Ni-Go Uranium enrichment (via thermal diffusion) program operated by the Army and the F-Go nuclear research program operated by the Navy. However, much like all other nuclear weapons research programs except those run by the Allies neither Ni-Go nor F-Go received the concerted allocation of resources that would have been required to make them effective in producing results during the war. Indeed, without the US's vast industrial resources, it's unlikely any other nation, especially a war-torn Japan, could have produced nuclear weapons under any circumstances during WWII.

It was only after the success of the Manhattan project that the effectiveness, practicality, and manufacturing cost of nuclear weapons became fully understood. Before then it was just a hypothetical superweapon. That the Allies were able to dedicate such a tremendous effort to the Manhattan Project is a testament to the enormous talent pool that had accumulated in the UK/US due to the brain drain from Nazi occupied Europe as well as to the equally enormous industrial capacity of the US economy.