Abstract: Despite its manifest material capabilities, Japan in Asia has been a non-leader or a sectoral leader at best. Starting from a working premise that Japan was not uninterested in enhancing its leadership position, the explanatory framework adopted here is centred on a regional source of socialisation as a mechanism to explain why the Japanese leadership has been limited in the first place, and why it has taken mainly ‘economic development’ as its purpose. The methodology proposed here takes role theory in foreign policy as the point of departure, but departs from it so as to follow the research agenda of a “more social” theory in international politics. It leads to a hypothesis that it is the structure of ideas at the sub-systemic level that limits Japanese leadership in Asia.