Both academics and journalists have given increasing attention to the rising importance of prime ministers – a phenomenon often referred to ‘presidentialization’. Although many commentators use the term differently, and the term blurs the line between the very different institutional contexts of a parliamentary and presidential system, one careful definition of the term is ‘the movement over time away from collective to personalized government, movement away from a pattern of governmental and electoral politics dominated by the political party towards one where the party leader becomes a more autonomous political force.’

This phenomenon has been observed primarily in Britain and in West European parliamentary democracies – no one has ever described the Japanese parliamentary system as even remotely ‘presidentialized’. In fact, the Japanese prime minister has not been the subject of much academic research, and even the Japanese press often used to ignore the prime minister. Despite being the leader of a majority party in a centralized political system, the Japanese prime minister was almost universally described as weak and uninteresting, with both academic and popular discourse focusing on the powerful bureaucracy and factional politics within the Liberal Democratic Party (LDP). However, recent political changes, most prominently the selection and popularity of Junichirō Koizumi as Japan's prime minister in the spring of 2001, have led to a surge of interest in the prime minister.