The world, especially the Asian world, is filled with generational conflicts and ancient grudges etc. Yet considering the sheer destruction they suffered at the hands of the Americans the local populace of Japan didn't doesn't seem to have immediately or ever had a period of sharp and widespread anti American sentiment or hatred. Then looking at how things developed between the two nations in the 50s and onwards relations actually got relatively warm all things considered. Is there any specific reason that the two nations grew so close so fast despite previously being at each other's throats to such a severity and that same generation that fought in or experienced the wars still a large part of the populace?
The immediate attitude of the Japanese people at the end of the war was that they put most of the blame of the war on their own leaders and military, not the United States. (Perhaps there was some ideological selection effect here — the most militaristic of the Japanese tended not to fare well over the long, deadly war.) In any event, these kinds of feelings were strongly encouraged by the United States, who as you will recall occupied and totally controlled Japan from 1945 until 1952. During that time, the Occupation not only coordinated a massive rebuilding and relief effort (always useful for winning hearts and minds) but also exercised dictatorial powers regarding the press. In this respect it worked very hard to try and silence any anti-American attitudes, and to discourage discussion of things like the atomic bombs in general.
Ultimately this seems to have had a very positive effect on Japanese attitudes towards the United States. One should not overestimate such things; there were, by the 1950s, significant frustrations with the United States, and the Castle Bravo incident in 1954 opened up discussion about Japan's status as an "atomic victim" in a very raw way. But even this became channeled less into an anti-American movement and more into an anti-nuclear, anti-war movement.
One can read the US efforts in Japan and West Germany in the postwar as a reflection of their main "lesson learned" from World War I: that if you ravage a nation and then keep punishing it after defeat, you end up with an enemy that, in a generation, will cause more strife. By contrast, in both cases the US sought policies that would uproot any latent anti-Americanism (or pro-militarism) while at the same time rebuilding, feeding, and helping. And in both cases the US willingly ceded their control to democratic governments, acknowledging the need for self-determination.
On the Occupation of Japan, see John Dower, Embracing Defeat. On the censorship work and the atomic bomb in particular, see Monica Braw, The Atomic Bomb Suppressed.