This article provides an innovative anthropological analysis of youth activism in contemporary Thailand by examining its past and current manifestations through an unusual theoretical nexus—that between (cosmological) politics and kinship tropes. Against the backdrop of the Buddhist kingdom’s long-standing cult of the ‘Father-King’, the article focuses on the 2020 Thai democracy movement in relation to student demonstrations in the 1970s. It aims to explore the ambiguous permutations in the meanings of kinship that have marked Thai young people’s democratic engagement in a range of social fields—including friendship, siblinghood, and comradeship. Drawing upon archival material, oral histories of student revolts, and extended ethnography with today’s youth activists in a number of political sites—anti-government rallies, universities, and private homes—the article reveals how kin relationships, hierarchies, and affects are entangled in diverse political formations of youth dissent. Through a detailed reading of these complex entanglements, it shows how relationships of ‘equal friendship’ and ‘hierarchical siblinghood’ substantiate the symbolic grounds of Thai youth activism, as conflicting instantiations of ‘filial insubordination’ to monarchical parenthood. While youth activists advocate for an egalitarian, ‘friendship-based’ polity, explicitly questioning the democratic viability of Thailand’s Buddhist kin(g)ship, they are simultaneously caught up in (seemingly inescapable) hierarchical sibling relationships that validate the latter’s ontological legitimacy in practice, generating subtle tensions. It is argued that attention given to the varied cultural shapes of these tensions can make it possible to unearth the deep, kinship-based core of Thai social conflict that is concealed beneath public forms and straightforward political stances.