In early 1942, the Imperial Japanese Army Air Force requested a replacement for the recently introduced Ki-43 fighter. The new aircraft had to match the Ki-43’s maneuverability, as well as the performance of modern Western fighters. It also had to feature powerful armament. Nakajima, the company that developed the Ki-43, took on the task. They set out to address the Ki-43's most significant shortcomings: insufficient armament, weak armor, and a climb rate. The new aircraft, designated the Ki-84, made its maiden flight in April 1943. It provided the fighter pilot with armor consisting of a backplate and bulletproof glass, as well as more powerful armament in the form of heavy machine guns and two 20 mm cannons. The aircraft met the previously established requirements, and the military wanted it so badly that prototypes were assembled in large quantities and were often identical. However, mass production did not begin until April 1944. The first production model was the Ki-84 Ko. This was followed by the low-production Ki-84 Otsu variant, with the most notable difference being in its armament of four 20 mm Ho-5 cannons. By the end of the war, 3,514 aircraft of various models had been produced.

The Ki-84 Otsu was introduced in Update 1.37. While it received enhanced armament compared to the Ko variant, the aircraft retained its strengths: an excellent climb rate, good dynamics, and maneuverability. However, it still has the same weaknesses: it quickly loses control at high speeds and is inferior to other Japanese aircraft in terms of maneuverability.