Ebook available to libraries exclusively as part of the JSTOR Path to Open intiative. This book explores the intersection of pop idol culture, social media, and nationalism in China, focusing on the role of fangirls in the 2019 Anti-Extradition Law Amendment Bill Movement in Hong Kong. By examining how algorithm- and data-driven platforms reshape fan culture and political participation, it highlights the transformation of seemingly apolitical fandom into highly politicized nationalist activism. Through in-depth interviews and digital ethnography, this book explores the gendered perspective of fangirls’ engagement, investigating how concepts of youth and nationalism, rooted in China’s modernization process, shape young women’s engagement with national identity and activism. It further examines how digital infrastructures enable large-scale mobilization, reinforcing both fandom practices and political participation. Evoking a historical perspective, it challenges the notion that fangirls’ nationalism is merely a product of coincidence, arguing that their political sentiments are deeply intertwined with their lived experiences in an era of economic reform. Ultimately, this book provides an updated understanding of Chinese nationalism, offering insights into interplay between digital media, youth culture, and political participation in contemporary China.