While planned for use in several promising aircraft, only prototypes were made and the engine never saw combat.
However, such ambitious targets necessitated extraordinary efforts and ingenuity at the same time.
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.