The Mitsubishi J8M Shūsui (Japanese: 三菱 J8M 秋水, literally "Autumn Water", used as a poetic term meaning "Sharp Sword", deriving from the swishing sound of a sword) is a Japanese World War II rocket-powered interceptor aircraft closely based on the German Messerschmitt Me 163 Komet.

The J8M1 was intended to be a licence-built copy of the Messerschmitt Me 163 Komet, but difficulties in shipping an example to Japan meant that the aircraft eventually had to be reverse-engineered from a flight operations manual and other limited documentation.

Japanese military attachés had become aware of the Komet during a visit to the Bad Zwischenahn airfield of Erprobungskommando 16, the Luftwaffe evaluation squadron charged with service test of the revolutionary rocket-propelled interceptor.

It is probable that the airframe was on the Japanese submarine RO-501 (ex-U-1224), which left Kiel, Germany on 30 March 1944 and was sunk in the mid-Atlantic on 13 May 1944 by the hunter-killer group based on the escort carrier USS Bogue.

The Japanese decided to attempt to copy the Me 163 using a basic instructional manual on the Komet in the hands of naval mission member Commander Eiichi Iwaya, who had travelled to Singapore in the I-29 and flown on to Japan when the submarine docked.

Two additional MXY8 gliders were constructed in the naval yard at Yokosuka, and one was delivered to the Rikugun Kokugijitsu Kenkyujo (JAAF Aerotechnical Institute) at Tachikawa for evaluation.

The JNAF also proposed a more advanced trainer, designated the MXY9 Shūka (秋火, "Autumn Fire"), which would be powered by a 2 kN (450 lbf) thrust Tsu-11 ducted-fan engine.

Mitsubishi and partners Nissan and Fuji proceeded with development of the airframe, and Yokosuka Arsenal was adapting the engine for Japanese production, designated the Ro.2.

The J8M1 had a wet weight that was 400 kg (880 lb) lighter, the aircraft having a plywood main spar and wooden vertical tail.

The Ki-200 and the J8M1 differed only in minor items, but the most obvious difference was the JAAF's Ki-200 was armed with two 30 mm (1.18 in) Type 5 cannon (with a rate of fire of 450 rounds per minute and a muzzle velocity of 920 m/s (3,000 ft/s)), while the J8M1 was armed with two 30 mm (1.18 in) Ho-105 cannon (rate of fire 400 rounds per minute, muzzle velocity 750 m/s (2,500 ft/s).

The Toko Ro.2 (KR10) rocket motor did not offer the same thrust rating as the original, and Mitsubishi calculated that the lighter weight of the J8M1 would not offset this.

On 8 January 1945, one of the two J8M1 prototypes was towed aloft, water ballast added in place of the fuel tank and rocket engine to test its aerodynamics.

Mitsubishi, Fuji Hikoki, and Nissan Jidosha all had tooling for mass production well into the advanced stages, ready to produce both the J8M1 and the J8M2 variant, which differed from the J8M1 in sacrificing one of the Type 5 cannon for a small increase in fuel capacity.

The Ki-202 was to offer improved flight endurance over the Ki-200 and was slated to be the priority fighter for the JAAF in 1946, but no metal was cut before Japan's surrender.

Nevertheless, the cost was deemed to be worth it, and plans were being drawn up to form a "Hagakure-Tai" (Special Attack Unit), similar to the German Sonderkommando Elbe, when the war ended.