The study investigates the potential of cloud seeding to mitigate extreme rainfall localization associated with mesoscale convective systems. Using a numerical weather prediction model, numerical cloud seeding experiments were conducted artificially increasing ice nuclei concentrations in a double-moment microphysics scheme for the heavy rainfall event. For a disastrous event that occurred in Japan in 2014, the authors show that idealized overseeding can suppress peak rainfall in high risk areas while producing an accompanying rainfall increase downwind. Estimates of the required amount of seeding substances in practical applications are provided.