At the time, Mitsubishi was working to promote a different engine, the Ha-42 (an 18-cylinder derivative of the Kasei), development of which was prioritized above the Ha-43's, delaying its completion. Consequently, the Ha-45 entered service first, albeit plagued with reliability issues, which would also trouble the Ha-43. Numerous promising aircraft, such as the Kyushu J7W interceptor and Mitsubishi's own A7M "Reppu" fighter, were planned to use the Ha-43, but in the end, such aircraft did not see service before Japan's surrender, nor did the engine itself.