Sports mega-events, like the Rugby World Cup, are often considered as a major platform for the celebration and reinforcement of nationalism. However, there is an emerging strand of research which contends that the host nations are increasingly presenting themselves with diverse, inclusive and cosmopolitan characteristics and, in turn, forms of nationalism have undergone some noticeable changes in more recent times. In this paper, we pursue an argument that Japan as the host of the 2019 Rugby World Cup projected the nation with a cosmopolitan outlook ultimately to sustain or even strengthen national interest and identity through the process of ‘cosmopolitan nationalism’. Methodologically, the research deployed critical discourse analysis to examine media representations of Japan as the host nation in general, and its national team in particular, within one of the leading Japanese newspapers as well as a range of other publicly available resources and materials in relation to the Rugby World Cup. In result, the study reveals the ways in which the discourse of ‘One Team’, embracement of foreignness and incidents of international exchanges during the event were mobilised to generate ‘thin’ cosmopolitan moments and, at the same time, were incorporated into the narratives of Japan's success on the world stage through conditional acceptance of foreignness and diversity. Consequently, this paper offers both a theoretical underpinning for and empirical evidence of the emerging linkage between sports mega-events and cosmopolitan nationalism.