Climate change has exacerbated extreme weather events, making coastal cities more susceptible to flooding, erosion, and related disasters. Since the mid-2000s, development pressures have been concentrated in coastal zones with high amenity and commercial value, resulting in high-density residential expansion on reclaimed land and within buffer zones designed for disaster mitigation. This study investigates how land-use deregulation affected development patterns and fragmentation in Busan, South Korea, from 2000 to 2023. Fragmentation indices were created on a 200×200 m grid framework (19,340 cells), and multiple regression and MANOVA analyses were used to assess the impacts of zoning changes on development density and disaster exposure. The results show that deregulation rate and area significantly increased patch number and density while decreasing average patch size, indicating increased fragmentation. Disaster exposure indicators, including population and impervious surface ratio, also increased with deregulation. The effects of deregulation were significantly stronger in coastal areas than in inland areas, indicating spatially uneven risk accumulation. These results show that deregulation facilitated urban expansion while also increasing vulnerability by concentrating high-density development in flood-prone areas. The study highlights the importance of land-use planning as a structural tool for addressing climate risks and guiding sustainable coastal development.