This chapter examines whether the advocacy of Japan’s civil society has changed after Fukushima, focusing on the policymaking process of the Nuclear Disaster Victims’ Support Law that took place in the period from April 2011 to June 2012. There are two main reasons why this law deserves attention. First, it is one of the few cases of so-called Diet Member bills, which are submitted by multipartisan politicians and differ fundamentally from most Japanese bills, which are drafted by bureaucrats and submitted by the cabinet. Second, its policymaking process showed successful advocacy by civil society organisations (CSOs), more specifically, increased CSO involvement in policymaking after Fukushima with respect to the following six aspects: (1) establishment and expansion of a CSOs’ network, (2) CSOs’ attempts to ensure the transparency of policymaking processes, (3) CSOs’ role as intermediaries between nuclear disaster victims and policymakers, (4) CSOs’ emphasis on the illegitimacy or legitimacy of national policies, (5) CSOs’ demands for accountability from policymakers, and (6) CSOs’ roles as sources of skills and expertise. The examination is mainly based on primary sources, such as protocols of the Diet sessions and documents published by ministries and politicians, as well as interviews conducted with CSOs and politicians.