This article conceptualizes South Korea as a movement-dependent democracy: a regime in which institutional stability recurrently relies on crisis-driven civic mobilization. In such systems, democratic resilience and institutional fragility coexist. Civic activism functions as a corrective mechanism when representative institutions falter, yet repeated reliance on mobilization may intensify polarization and expose limits in institutional absorption. By analyzing delegative presidentialism, fandom politics, cleavage stacking, and crisis-driven mobilization, this study contributes to comparative debates on democratic erosion and resilience. The Korean case demonstrates that democratic defense and democratic vulnerability can unfold simultaneously within the same regime. Rather than reducing mobilization to either democratic vitality or populist destabilization, this study shows how democratic defense and democratic vulnerability can coexist within the same institutional order.