In early 1943, as the war situation worsened, Nakajima had to develop a very long-range
Fugaku bomber which
could be able to mount bombing raids against targets along America's western
seaboard. The Fugaku project impressed the Japanese Army and Navy.
was deemed too complex, and would
not be available in service. The Japan Army shifted quickly away from
the project and sought to other possible development from Kawasaki.
Kawasaki began investigating a four-engines bomber design which compared
configuration to the American B-29, it was proving to be a superior
airplane to the best of the bombers then in service. The design was
accepted and was given designation Ki-91. A flying prototype was started
from a drawing board but progress was slow by lack of required
materials. In February of 1945, the Ki-91 prototype was partially
completed but work was forced to cease, as all the facilities to
complete the Ki-91 in Kawasaki's plant were destroyed by bombing raids