A big 'if' because Japan's technology in World War II was primitive. They were excellent at building on the Western technology they imported in the 1930s, and could improve on it. But they lacked the fundamental industrial technique needed to take that 'next step'.
So, for instance, they struggled to replace their early war fighter planes because they could not manufacture engines to the fine tolerances necessary to match the US and European aircraft. Their radar was always very primitive, or non-existant. Japan would have attacked the USA.
Late in the war there were plans to attack the Panama canal with planes launched from large submarines, and perhaps they could have delivered a weapon this way. The Japanese were clearly frustrated by their inability to effectively attack the American mainland, but they certainly held a view that Americans were 'soft' and would surrender if they could be shocked. With the USA out of the war, the Japanese were confident they could defeat China and hold off the British.
If the Japanese had developed the atom bomb during World War Two - and it's a pretty big if, since they lacked the industrial capacity even to supply enough tanks, planes and ships to their own forces - then I'm not sure they would have attacked the cities in either country. The logical thing to do with an atom bomb during 1944 or 45, when the Allies are practically knocking on the front door of Japan, is to drop it either on the US Fleet - if you can find it - or on one of the recently captured islands like Iwo Jima or Saipan, to prevent it being used as a base for the conquest of the Japanese mainland.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.