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The Nakajima Ki-44 Shoki (Demon or Devil-Queller) interceptor was the only interceptor fighter serving with the Japanese Army when the B-29 campaign against Japan began. At that time, it was the fastest-climbing Japanese fighter in service, and was one of the few aircraft capable of reaching the B-29s at the altitudes at which they operated.

The Ki-44 Shoki originated in parallel with the Ki-43 Hayabusa (Peregrine Falcon) single-seat fighter. At the same time that Nakajima was working on the initial design of its Ki-43 single-seat fighter for the Japanese Army, the Koku Hombu (Air Headquarters) issued a specification for Nakajima to begin work on an interceptor as a parallel project. This project was assigned the Kitai number of Ki-44 (next in line from the Hayabusa Ki-number). Unlike previous Japanese combat aircraft design philosophy, it was decided that the Ki-44 was to be built strictly as an interceptor, with emphasis being placed on speed and climb rather than on maneuverability. The specification called for a maximum speed of no less than 373 mph at 13,125 feet.

This altitude was to be attained in a time no greater than 5 minutes. Armament was to consist of a pair of 7.7-mm and a pair of 12.7-mm machine guns.

The design team was directed by Najajima's project engineer, T. Koyama. The engine selected for the new interceptor was Nakajima's own Ha-41 fourteen-cylinder double-row radial. This engine had actually been intended primarily for bomber aircraft, and had a rather large diameter. Nevertheless, the design team was able to marry this engine to a fuselage of narrow cross section, producing an aircraft which always looked to me like it had "too much engine". The fuselage was designed with a large side area to help ensure a stable gun platform. The fin and rudder were mounted well to the rear of the horizontal tail. The vertical tail has always looked to me as though it was "too small", but this is undoubtedly a misperception. The wing area was relatively small for an aircraft of the size and weight of the Ki-44, leading to a high wing loading and a relatively high landing speed. A set of "butterfly" combat flaps were fitted for improved maneuverability.

Nakajima began development of the Ki-44 in 1940 as a pure interceptor with emphasis being placed on airspeed and rate of climb rather than maneuverability. The Japanese Army Air Force specification called for a maximum speed of 600 km/h (370 mph) at 4,000 m (13,130 ft), to be attained in five minutes. A set of Ki-43-like "butterfly" combat flaps was fitted for improved maneuverability. Armament consisted of a pair of 7.7 mm (.303 in) and a pair of 12.7 mm (.50 in) machine guns.

The engine selected for the new interceptor was Nakajima's Ha-41 (a development of the Nakajima Ha-5) 14-cylinder double-row radial, originally intended for bomber aircraft. Although the Ha-41 was not the ideal choice due to its large-diameter cross section, the design team was able to marry this engine to a much smaller fuselage with a narrow cross section. At 1,260 mm in diameter, the Ha-41 was 126 mm larger in diameter than the 1,144 mm Nakajima Sakae (used in the Mitsubishi A6M "Zero" and Nakajima Ki-43 "Hayabusa"). However, the Sakae was only 27.8L in displacement and 1,000 hp, while the Ha-41 was 37.5L and made 1,260 hp (1,440 in the later Ha-109 version). In any case, since the Sakae wasn't powerful enough, the only alternative available was the Mitsubishi Kinsei, which was slightly smaller than the Ha-41 in diameter, five liters smaller in displacement, and was less powerful. Unfortunately, this was already in demand for many other aircraft, so the Ha-41 was chosen as the best powerplant. In order to achieve its design goals, the wing area was relatively small leading to a high wing loading and a comparatively high landing speed that could be daunting to the average Japanese pilot, who was more used to aircraft with a low wing loading like the Ki-44s predecessors, the Ki-43 and Ki-27.

The first Ki-44 prototype took to the air for the first time in August of 1940. The prototype was armed with two synchronized 7.7-mm Type 89 machine guns in the upper engine cowling and one 12.7-mm Type 1 (Ho-103) machine gun in each wing outboard of the main undercarriage leg. The first test flights were generally encouraging, and handling was considered rather good despite the high wing loading. However, the landing speed was somewhat greater than that for which most Japanese pilots were accustomed, and the big engine restricted the forward visibility while the plane was taxiing on the ground. However, the inflight visibility was considered as being excellent.

Unfortunately, the performance of the Ki-44 was below that called for in the original specification. Maximum speed was only a disappointing 342 mph at a weight of 5622 pounds. It took 5 minutes 54 seconds to reach an altitude of 16,400 feet. A series of modifications were made to the prototypes to increase the performance and reduce the drag. The rigidity of the engine mount was modified, the supercharger intake was revised several times, and the cowling flaps were changed. Thus modified (and with armament removed), the maximum was up to 354 mph, still below specification. The firewall installation was then modified to improve the engine cooling, thus making it possible to remove the five cooling vents mounted on each side of the forward fuselage just aft of the cowling gills. With these vents sealed up, drag was substantially reduced and speed was now 389 mph (still without the armament). This speed now exceeded the original specification. Although this speed had been achieved with an unarmed plane, calculations indicated that production aircraft with armament fitted would be able to reach a maximum speed of 360 mph, and the Japanese Army deemed that this was good enough to make the aircraft fit for production. The design was accepted by the Japanese Army for service under the designation of Army Type 2 Single-seat Fighter Model 1 (Ki-44-I). It was given the popular name of Shoki, which means "Demon" or "Devil-Queller", depending on which reference you pick up.

Seven pre-production aircraft were built, the last being delivered in September of 1941. The armament was the same as that of the prototypes--two 7.7-mm machine guns in the engine cowling and two 12.7-mm machine guns in the wings. The guns were aimed by a telescopic gunsight which protruded through the windshield. The original 3-piece cockpit canopy (in which the front and rear pieces were fixed and only the center section slid backwards) was replaced by a two-piece canopy in which the entire rear section slid backwards. The radio mast was moved from a mounting on the cockpit to a position on the starboard side of the forward fuselage, and the rudder was redesigned. Provision was made for two 28.6 Imp gall drop tanks carried underneath the wing center section.

The pre-production aircraft and two of the prototypes (which had been brought up to pre-production standard) were turned over to the Army for service trials on September 15, 1941. They were handed over to an experimental squadron, the Kawasemi Butai, for service trials. The unit was sent to China for combat trials, and in May 1942 was renamed 47th Dokuritsu Dai Chijugo Chutai. In September of 1942, all tests were completed and the type was accepted for service with the JAAF.

The Nakajima Ki-44 at one point equipped 12 sentai ("groups/wings") of the Imperial Japanese Army Air Force: 9, 22, 23, 29, 47, 59, 64, 70, 85, 87, 104 and 246 Sentai. The Manchukuo Air Force also operated some Ki-44s.

Pre-production Ki-44 aircraft and two of the prototypes were turned over to the Army for service trials on 15 September 1941. The type commenced operations when nine aircraft were received by an experimental unit, 47th Chutai "Kawasemi Buntai" ("Kingfisher Flight, 47th Squadron"), commanded by Major Toshio Sakagawa at Saigon, Indochina in December 1941.
The Ki-44 also saw significant action with 87th Sentai in the air defense role, while based at Palembang, Sumatra. Other units equipped with the Ki-44 during the early part of the war were stationed in China, Burma, The Philippines and Korea.

Later in the war, the type saw action in an air defense role over the home islands - mainly around Japan's large industrial cities. 47 Chutai, after it was transferred to air defense roles in Japan, was expanded to become 47 Sentai.

The Ki-44-II Otsu (also known as the Ki-44-IIb) could be armed with a Ho-301 40 mm autocannon. While this was a relatively high-caliber weapon, it used caseless ammunition with a low muzzle velocity and short range, which was effective only in close attacks. Some of these aircraft were used against USAAF bombers by a special Shinten Seiku Tai (air superiority unit), comprising at least four aircraft, that was part of 47th Sentai, based at Narimasu airfield in Tokyo. Pilots from such units attempted to shoot down B-29s and, once their ammunition was expended, to ram them - effectively a suicide attack. While the concept appeared straightforward, ramming a B-29 at high altitudes was difficult to achieve in practice.

By the end of the war, Ki-44 variants were being replaced by the Nakajima Ki-84 Hayate, which was regarded as vastly superior - in aspects other than maintenance and reliability.

During 1946-49, both sides in the Chinese Revolution operated Ki-44s surrendered or abandoned by Japanese units. Air units of the People's Liberation Army obtained aircraft formerly belonging to 22 and 85 Sentai, which had disbanded in Korea. Some of these aircraft were reportedly flown by Japanese veterans. Within the Republic of China Air Force 18th Squadron (12th Fighter Group) was equipped with Ki-44s formerly of 9th Sentai, which had disbanded in Nanking, and 29th Sentai, which had disbanded at Formosa and they saw action in . Following the People's Liberation Army Air Force (formed in 1949) used the Ki-44 until the early 1950s.

Three variants of the Model 1 were produced, the Ki-44-Ia, Ib, and Ic. They differed primarily in armament and in minor equipment changes. The Ki-44-Ia was fitted with 2 7.7-mm machine guns in the fuselage and two 12.7 mm machine guns in the wings. The Ki-44-Ib was armed with four 12.7-mm machine guns (two in the fuselage, two in the wings), and had the oil cooler moved to a position under the cowling gills. The Ki-44-Ic had similar armament to the Ib, but had the lower hinged portions of the main wheel fairings moved from the landing gear legs to the fuselage.

The Shoki was first encountered by the Allies over China. It was assigned the code name Tojo by Allied intelligence working in that theatre. This name was a departure from the standard Allied coding convention, in which boys' names were assigned to Japanese fighters. However, a special request was made that the Tojo name should be allowed to stick, and all coordinating Allied intelligence agencies readily agreed. A total of about 1225 aircraft were built. No complete surviving examples of the Ki-44 exist.