The Ki-61-I hei (丙), designated Type 3 Fighter, Model 1C (三式戦闘機一型丙), was the third variant of the Kawasaki Ki-61 series, produced in parallel with the previous otsu model from September 1943 and continuing until July 1944. The primary difference was the replacement of the wing-mounted machine guns with imported German Mauser MG 151/20 cannons, adopted as a stopgap measure while the Japanese Army lagged in domestic 20 mm aerial cannon development and production. These cannons gave the aircraft its distinctive appearance, with the barrels noticeably protruding from the wing leading edges. Within Kawasaki, the variant was sometimes referred to as the Ki-61 Type Ma (マ), derived from the Japanese pronunciation of Mauser (マウザー). However, the additional weight of the cannon installation and ammunition resulted in a slight reduction in overall flight performance compared to earlier variants.

The Ki-61-I hei has been in the game since the start of the Open Beta Test prior to Update 1.27. It represents the most heavily armed Ki-61-I variant, trading a small amount of flight performance for significantly improved firepower. The two 20 mm MG 151 cannons deliver strong burst damage and reliable destructive capability against both fighters and bombers, greatly increasing lethality compared to the machine gun-armed kō and otsu models. Even with the slight performance drop, the aircraft retains the Ki-61’s characteristic stability, good diving ability, and respectable speed at medium altitude. It performs best when used in boom-and-zoom or energy-fighting tactics, leveraging its improved armament to finish engagements quickly rather than committing to prolonged dogfights.