The R2Y1 had a 45.93 ft (14 m) wingspan and was 42.81 ft (13.05 m) long. The aircraft stood 13.91 ft (4.24 m) high, weighed 13,260 lb (6,015 kg) empty, and had a maximum weight of 20,725 lb (9,400 kg). The Keiun had an estimated top speed of 447 mph (720 km/h) at 32,810 ft (10,000 m) and a cruise speed of 288 mph (463 km/h) at 13,125 ft (4,000 m). Maximum range was an estimated at 2,240 mi (3,610 km). The pilot sat under a raised bubble-style canopy that was toward the extreme front of the aircraft. The radio operator/navigator occupied an area in the fuselage just behind and a little below the pilot.
The Keiun was powered by two 60-degree, inverted V-12 Aichi Atsuta 30 engines (licensed version of the Daimler-Benz DB 601) that had been uprated and were coupled together by a common gear reduction. The resulting 24-cylinder power unit was known as the Aichi [Ha-70] 01. With a 5.91 in (150 mm) bore and 6.30 in (160 mm) stroke, the engine displaced 4,141 cu in (67.8 L) and was installed behind the cockpit and above the wings. The Aichi [Ha-70] 10 (some say [Ha-70] 01) engine was to be turbocharged and rated at 3,400 hp for takeoff and 3,100 hp at 9,845 ft (3000 m). The engine drove a 12.47 ft (3.8 m), six-blade propeller via a 12.8 ft (3.9 m) long extension shaft that ran under the cockpit. Engine cooling was achieved by radiators under the fuselage and inlets for oil coolers in the wing roots. A ventral air scoop was located behind the engine to provide induction air for the turbocharger and air for the intercooler.
