A poll has found that 82% of the Japanese public has a positive/friendly feelings towards the United States:
While the United States has consistently scored highly in the Cabinet Office’s annual poll of attitudes toward foreign countries, the latest result was the highest since the survey began in 1978. Only 16 percent of respondents reported not having a friendly attitude toward the United States, the lowest such result ever.
Some of the credit for this rise can be attributed to Operation Tomodachi, the massive disaster relief mission that the United States military launched after the March 11th earthquake and tsunami hit Tohoku. The American military is continuing to provide assistance to disaster victims, and has been getting positive Japanese media coverage all along the way.
As this graph shows, there was also a small increase in friendly feelings towards China (but not enough to recover from the damage caused by aggressive Chinese actions in 2010):