The polls I have seen for postwar Japan indicate that they blamed the military for World War II and its disastrous consequences in general, of which the atomic bombings were only one component. I have not seen any that make it seem like a large number blamed the Emperor, and even in the case of the military I have not seen anything that made it seem like people were seeking retribution so much as an understanding that one should not let the military run one's country (which they did not need to enact, since the US Occupation undid that). There was, during the years of US Occupation, very little public discussion of the atomic bombings, because the US suppressed such speech in an effort to turn the Japanese into pro-US allies, and so that might have had something to do with it. In the 1950s, after the Occupation ended and there started to be conversations about these things publicly, the Japanese attitudes towards nuclear weapons were either directed towards an antipathy to war itself, or towards the United States.

On Hirohito himself, a great effort was made on his behalf in the postwar to make it appear that he had nothing to do with the war and was opposed to it from the beginning. It's not as clear-cut as that in real life, but both Hirohito and his supporters, and later the US Occupation, saw value in making this kind of argument as a way to preserve Hirohito's status among the Japanese and his utility to the occupying powers.

Dower's Embracing Defeat touches on all of this, for further reading.