This ethnographic study offers a comprehensive examination of the Namahage, a ritual tradition unique to Japan's Oga Peninsula in which masked figures descend upon households on New Year's Eve to admonish sloth, instill moral discipline, and reaffirm communal values. Far from mere folklore, the Namahage embody a living cultural system that integrates ritual performance, symbolic fear, agricultural cosmology, and evolving local identity. Through historical analysis, participant observation, and cross-cultural comparison, DiCristofano investigates the Namahage's shifting function within both rural lifeways and the broader politics of cultural preservation. The work considers themes of social conformity, performative authority, intergenerational transmission, and the ritualized use of fear as a pedagogical tool. It further explores how state recognition (including UNESCO Intangible Cultural Heritage designation) has shaped public narratives around the Namahage, raising questions of authenticity, commodification, and resilience. Combining rigorous scholarship with evocative prose, Namahage: Guardians of Northern Japan situates the Namahage within the larger discourse of ritual studies, Japanese folklore, and the anthropology of moral culture.