The Kawasaki Ki-88 is an odd bird aircraft, much like the J4M a tier above it.
Developed due to delays in the production of the Ki-64 the Ki-88 was based heavily upon the design of the Bell Aircraft P-39 Airacobra, with an engine mounted mid fuselage with a 37mm cannon firing through the prop spinner. A mockup of the design was completed and evaluated. Its expected performance was equal to the Ki-61 Hien which was already operational and the program was scrapped.
The "Bruce" as I call her is a high flying energy fighter from a nation that is known for low to mid altitude turnfighters, so every tactic used by Zero jockeys is of less value in this beast. The Ki-88 is almost a Japanese Mustang and will reward pilots who are experienced in Mustang and MiG play and blend the tactics of energy fighting with the turning ability possessed by the Bruce.
That is what determines your success in this aircraft; recognizing which aircraft the Bruce should boom n zoom and which aircraft it should draw into a turning dogfight. In either case gun discipline is necessary for good results. The Ki-88 has a frightening collection of cannons mounted center mass. They have low muzzle velocity so they are only accurate at close range but the amount of damage they crank out allows the Bruce to decimate almost anything with one overheat cycle and makes her a serious threat to heavy fighters in the early game and ground attackers in the end game.
Bear these fundamentals in mind and the Ki-88 will serve you well indeed.
Good hunting!