Strongest Japanese Piston Fighter

The Rank VIII blueprint aircraft, J6K1 Jinpu, is genuinely top-tier for its BR. It's not particularly strong against ground targets, but with 250kg bombs, it can destroy bunkers. It's an easy-to-handle aircraft with absurd armament of six 20mm cannons and two 13.2mm machine guns, coupled with high maneuverability. Its defense is surprisingly tough; it can take hits despite not having any special armor. The downsides are poor acceleration and weak sustained/vertical turning due to its weight and engine characteristics. You'll have a tough time if you don't gain altitude by flanking or dive. However, its weight means tremendous energy in dives, making it quite strong in that regard. Facing F-89Ds or Tu-4s is pretty scary, but I believe it's the strongest regardless of nation. It's an aircraft you won't regret purchasing, even if it takes time.