On 2 August 2020, a coastal bow-echo mesoscale convective system (MCS) produced severe rainfall and damaging winds over South Korea, resulting in casualties and property losses. Forecasting rapidly developing coastal bow echoes remains challenging due to limited understanding of the interactions between mesoscale dynamics and microphysical processes. Here, we analyze these interactions using improved multi-Doppler wind retrievals and polarimetric radar observations. The system evolved into a leading convective–trailing stratiform structure, reinforced by a rear-inflow jet (RIJ) that enhanced low-level convergence and shaped bowing segments. Feedbacks between RIJ-driven downdrafts, convective updrafts, and hydrometeor recycling sustained precipitation and prolonged the system’s lifetime after landfall. In particular, mixed-phase hydrometeors in stratiform clouds were advected into the leading convective line, where they enhanced and maintained deep convection. These dynamic–microphysical interactions governed storm organization and rainfall efficiency, explaining the persistence of heavy precipitation in the coastal zone. Beyond advancing process understanding, our results highlight the role of land–sea contrasts in shaping mesoscale circulations that intensify convection and provide observational benchmarks for improving forecasts and hazard resilience in coastal regions.