A high-power input coupler was developed at KEK to deliver 100 kW-class radiofrequency (RF) power in the continuous-wave (CW) mode at 1.3 GHz to a superconducting cavity. To mitigate thermal loads during high-power RF transmission, the coupler was engineered with active water cooling integrated into critical components, including a warm inner conductor, outer conductor, antenna, and RF window. The newly developed coupler underwent RF conditioning of up to 145 kW in the pulsed mode and 100 kW in the CW mode using dedicated test stand at room temperature. The coupler successfully transmitted world-record CW 100 kW RF power at 1.3 GHz continuously for 10 h without any interlock event. During operation, the temperature rise of the warm inner conductor, the most thermally stressed component, was limited to 15 °C whereas the maximum observed temperature increase was 19 °C at the doorknob. Further power scaling was not constrained by the coupler itself. These results demonstrate that the newly developed coupler can reliably sustain CW RF transmissions exceeding 100 kW with excellent thermal performance.