We present a comprehensive evidence on how the Japanese reacted to the sudden death of North Korea's Kim Jong Il in December 2011, which was an event of enormous significance for Japan's national security. Based on our original, partially panel-structured, multi-wave monthly surveys conducted from December 2011 to March 2012, we analyze how the Japanese learned about his death, how they formed evaluations about its implication, and how their perceptions changed over time. Our findings illustrate that Japan's general public reacted in a remarkably calm and balanced way to the evolving situation, pointing to a basic sense of realism that underlies their attitudinal orientation toward North Korea. This sense, we argue, derives from the confidence widely held in Japan that, while North Korea remains one of the crucial sources of external threats, its overall ability to influence the regional and international dynamics is limited and its threat thus containable within current framework of national security.