I have to go with GrG and say it was the N1K2-J Shiden-Kai, Allied Code Name: "George"......
The plane was just unreal in its flight performance, and when American test pilots first flew it, the couldnt compare anything in the US arsenal to it, because there was nothing we had that was close.....
A plane flown by the best Japanese pilots they had left......
Four wing-mounted 20 mm Type 99 Model 2 cannon (N1K1-Ja, N1K1-Jb, N1K1-Jc, N1K2-J, N1K2-Ja and N1K2-K)....
One Nakajima NK9H Homare 21 eighteen-cylinder air-cooled radial, rated at 1,990 hp for take-off, 1,825 hp at 1,750 m and 1,625 hp at 6,100 m, driving a four-blade metal propeller (production N1K1-J, N1K2-J, N1K2-K, N1K3-J and N1K3-A)....
The Shiden Kai was to become the best all-round fighter to be operational in the Pacific theatre.... It was fast, powerful, and maneuverable, and was well-armed and armored...... In the hands of an experienced pilot, the Shiden-Kai was the equal of any Allied fighter, even the later models of the P-51D Mustang which began to appear over Japan in the spring of 1945......
In one notable action, on February 16 1945 over Yokohama, Warrant Officer Kinsuke Muto of the 343rd Kokutai in an N1K2-J single-handedly battled a dozen F6F Hellcats...... He shot down four of them before the rest were forced to break off combat and return to their carrier......
The Shiden Kai had its center of gravity just alittle too far aft, and to correct this problem the N1K3-J Shiden Kai 1 Model 31 was built, which had the Homare 21 engine moved forward six inches..... This freed up enough space to permit two 13.2-mm machine guns to be fitted in the engine cowling..... Two prototypes were built at Himeji, but this model was never put into production....
Only 415 production examples of the outstanding N1K2-J fighter were built, owing primarily to construction snags and delays resulting from the continuous B-29 raids on the Japanese homeland in the last year of the war..... With the exception of Kawanishi's Naruo and Himeji plants, the other companies involved in the production pool were late in getting started and delivered only a token number of machines before the war ended.....
It is fortunate for the Allies that this outstanding aircraft was not available in greater quantity.