"but because they focused on the death ray made by tesla"
The what?
Japan had no chance of developing an atomic bomb in WW2. Nuclear physics was not the product of a single country or person working in isolation, it wasn't possible even for the US to build an A-bomb much before when it did without a significant number of PODs across several scientific disciplines going back years.
And to get back to the first question, what Japanese death ray programme? Tesla's death ray proposal was unscientific baloney with no basis in reality. If there were a couple of Japanese physicists in the 1930s deluded enough to be working on Tesla's mad idea (Tesla did not make a death ray and no "but what if he did" POD short of changing the laws of physics would lead him to it) then that's not a research programme and redirecting that effort to nuclear research would have no effect.
Even if it was physically impossible it doesn't mean that the Japanese couldn't have wasted money on it thinking it was real.