The chapter investigates the new roles that media play in the representation of politics and popular culture in Japan in the post 3.11 period. Combining ethnography, interviews, and detailed examination of key media moments, we outline the Students Emergency Action for Liberal Democracy’s (SEALDs) sophisticated use of the mass media that led to legitimation and unprecedented levels of mobilization at demonstrations against controversial security legislation from May 2015 until August 2016. In contrast to much of the existing literature on social movements, we show how social media have not replaced mass media but how SEALDs used social media in a more complicated way to insinuate themselves into the mass media flow through social media. Theoretically, this case allows us to challenge the view of the relationship between social and mainstream media found in other studies, arguing for a co-constitutive view, rather than a sequential view of social media supplanting mass media. The SEALDs case also demonstrates the dangers faced by any social movement organization (SMO) around the loss of control of their messages and images when absorbed into the personality-driven mass media that tend to blur the lines between politics and culture, engagement and entertainment.