Designers from time to time to enjoy the freedom to develop their vision and direction from the drawing board to the tarmac, with which the aircraft is ready to climb into the sky. Powered by Takeo Kawasaki Dio was just such a designer. Despite the very real work in the development, testing and production of military aircraft for the IJA, Doi disposal concept, which he put forward at its own discretion to the forefront. Initially, the IJA did not want to hear about the project, but later, when the Ki-64 began to be translated into concrete forms, their opinion has changed. In 1939, Doi has been associated with the two programs Kawasaki: Ki-45 Toryu and Ki-60 / Ki-61 Hein. Ki-45 aircraft proved terribly difficult: the problem with the chassis, excessive resistance, difficulties with engines and other troubles were headache firm Kawasaki. These problems, tormented earlier version of Ki-45, decided Doi. In addition to working with wallowing in the Ki-45 issues in 1940, he was associated preparatory work on the Ki-60 interceptor and tactical fighter Ki-61 Hein. Even with such duties Doi developed its own high-speed fighter, initially considering it a pure experiment in achieving high speeds. His concept of high-speed aircraft included a number of new features that are perceived as quite unusual compared to traditional with other more traditional types. Since Doi plane was proprietary and not create to meet any specification, he was disappointed by the fact that when the IJA IJA banned Kawasaki to give some more time to the project.