In November 1943 the Rikugun Kokugijutsu Kenkyujo (Army Aerotechnical Research Institute) suggested that the Ki-67, then undergoing flight trials, be modified to be a hunter killer. The Ki-109a would be the killer with obliquely mounted 37 mm cannons and the Ki-109b would be the hunter with radar and a search light.
Major Sakamoto came up with the idea of putting a 75 mm Type 88 anti-aircraft gun in the nose. It was thought it could shoot at the B-29s while staying out of the range of their defensive armament.
Engineer Ozawa led the team that completed the first prototype of a modified Ki-67 with a 75 mm gun in the nose.
After the third aircraft the dorsal turret, later blisters and bomb bay were not included.