Why did Japan actively promote the revival of the Japan-US-Australia-India Quadrilateral Security Dialogue (Quad) as its new regional cooperation platform? And How could they succeed in convincing others to join? This article focuses on the shift in Japan's pursuit of reputation in the security realms and the need to balance against China as US's presence in the region is in relative decline. In this article I insist that the change of Japan's pursued reputation from ‘non-military power’ to ‘reliable security partner’ in the regional/international community is the reason that Japan could convince other regional partners and lead the revival of Quad. This argument is based on the logic of the cooperation and reputation. Cooperation needs information about potential partner's intention, and reputation of potential partners contains observable information, especially whether they are trustful or not. In other words, reputation is an important causal mechanism for emergence of multilateral cooperation, especially when it comes to the question of ‘whom to cooperate with’. This is the reason why Japan's reputation or change of the reputation is key to the emergence of Quad.