In March 1937 / 1937 the Japanese Army issued a requirement for a two engine fighter.
Kawasaki (Ki-38), Mitsubishi (Ki-39), and Nakajima (Ki-37) also submitted designs as well, but the Nakajima was selected. Kawasaki submitted the Ki-38 which would later become the Ki-45.
Takeo Doi / Isamu Imashi worked on a design, starting in January 1938, that would help with production. A mockup was ready in October 1937. This lead to the Ki-45 Kai.
In December 1937 new specifications were given for the Ki-45.
- Speed: 340 mph at 10,000' , 335.5 mph / 540 kph at 11,480' / 3,500 m
- Operational Altitude: 6,500' to 16,250', 6,560' / 2,000 m to 16,505' / 5,000 m
- Cruising Range: 4 hours and 40 minutes at 217 mph / 350 kph / 220 mph
- Armament: Two forward firing and one rear firing machine guns
- Engines: Two Nakajima Ha-20b
Takeo Doi became the chief engineer in January 1938 and in January 1939 the first prototype was ready.