The Mitsubishi J8M Shusui was a copy of the Messerschmitt Me. 163B, which the Japanese got license rights to manufacture.
A German submarine, which was transporting a Me 163, was sunk by the Allies. This only left the plans and an engine for the Japanese to use.
The Imperial Japanese Navy put out a 19-Shi specification for a rocket powered jet fighter. Mijiro Takahashi of Mitsubishi lead the design effort and by September 1944 a mock-up was completed.
Army Navy Cooperation
The J8M project was one of the few that the Army and Navy cooperated on. Technicians from both services worked on building the engine.
However, each then ordered separate glider trainers to be built. Maeda Koku Kenkyujo (navy) and Yokoi Koku K.K. (army) built around 50 of the glider trainers.
Rikugun Kogugijutsu Kenkyujo developed the Ki-202 which was to be the Army version.