In the summer of 2012, the usually desolate sidewalks in front of the prime minister's official residence (Kantei-mae), the Japanese equivalent of the White House, became the stage for a weekly antinuclear protest that claimed turnout in the hundreds of thousands to become the definitive symbol of political life in a country still reeling from nuclear disaster. Protesters, most of whom demonstrated for the first time in their lives, gathered here for two hours every Friday evening to “make visible the will of the people” to the Prime Minister in his own residence. When successful, such populist performances appeared to participants and spectators alike as nothing less than a manifestation of “the people” itself.Populism, as I approach it here, imagines such moments as deeply meaningful, in that they do not just claim to express, but carry the potential to directly embody the will of “the people.” As an ethnography of mass protests and the organizing efforts behind them, my dissertation asks how such populist imaginaries are expressed in protest rhetoric and strategy, and how new endeavors to envision and embody “the people” as a locus of political legitimacy came to the forefront in the aftermath of the Fukushima Daiichi nuclear meltdowns. As I attend to this endeavor ethnographically, I reach for a critical notion of the “legitimacy” of mass protest as one tangible aspect of protest organization and participation — legitimacy, that is, not “from above,” as the right or acquiescence to rule, but asserted “from below” in terms of the relation between mass protest and a broader public. Postdisaster populism, in this sense, posits the figure of “the people” as both wellspring of legitimacy and antidote to a decades-long distaste for mass protest in Japanese society. Scholars and pundits alike have held up the Kantei-mae crowd as a symbol not just of legitimate assembly, but of the postdisaster period as a renaissance of political agency and expression. What was it about this embodiment of populist legitimacy that succeeded in summoning unparalleled multitudes in front of the Prime Minister’s official residence — and why did it ultimately fail to gain traction with the wider populace, and shatter into disunity and discord just like the illegitimate precursors it tried to distance itself from? This dissertation asks how the endeavor of enfleshing the figure of “the people” in stringently surveilled public spaces came to constitute both impetus and “imaginative horizon” for new formulations of political legitimacy, agency and subjectivity in postdisaster Japan. Who can speak in the name of the people? What voices have been left out of this claim to univocality, and what sorts of violence have been sanctified in its shadow? By asking these questions from within the effervescence of the crowd amassing again and again in Japan’s symbolic center of political authority, my ethnography seeks to contribute to a critical understanding of democratic participation in an age of resurgent populist fervor.