People hold slogans during a protest against Barack Obama's visit to Japan, in Tokyo, Japan, April 23, 2014. Obama arrived in Japan on a four-country trip through the Asia-Pacific region on Wednesday. (Xinhua/Yan Liang)

A man with a mask of U.S. President Barack Obama attends a protest against Obama's visit to Japan, in Tokyo, Japan, April 23, 2014. Obama arrived in Japan on a four-country trip through the Asia-Pacific region on Wednesday. (Xinhua/Yan Liang)