Driven by the increasing need for coastal protection under climate change and the growing demand for renewable energy, integrated concepts that combine coastal protection with wave energy harvesting have attracted increasing attention. In this study, we propose a semi-cylindrical rotating-buoy-type wave energy converter installed at the front of a floating breakwater and experimentally investigated its dynamic response characteristics. Hydraulic model experiments were conducted under regular wave conditions. The buoy motions were quantified by video-based motion analysis, and the response amplitude operators for heave and pitch were determined. The results revealed a transition in the dominant motion mode with increasing wave period. Heave response is more pronounced in short-period waves, whereas pitch response becomes dominant under long-period wave conditions. These findings suggest that the design of floating bodies and moving-body-type wave energy converters should account for site-specific wave characteristics. Motion-oriented designs considering the dominant response mode may contribute to the more efficient optimization of wave energy conversion systems.