This alternate time line was suggested to me many years ago by my Uncle, who was a pilot officer in the IJAF.
Basically, there was a sizable group in the IJ military that did not like the Germans, and thought the best way to go was with the Brits. Many had been educated in British Universities and had great respect for the British Culture.
Now...it's June 1940, and England is in it's darkest hour.
POD - Tojo and his cronies in the Black Dragon Society are overthrown or at least shunted aside, and a surprising offer is made to England.
The new government of Japan, in return for free market access to raw materials such as oil, rubber and steel, will repudiate the Axis Treaty and send military assistance to England, starting with the Carrier Battle Groups.
Despite deep suspicion, and under heavy escort, the Japanese Carriers come up through Suez and begin fighting the Italians and Germans with fierce determination.
They get the free market prices they ask for, and both sides keep the bargain. Pretty soon, freighters of IJAF fighters begin unloading at Western British Ports and joining the Naval Brethern and the RAF, against the Luftwaffe
The war in the Pacific never really happens, and the war in China thins out and dies as Japan gains the trust and support of her new Allies. An uneasy peace is forged between Japan and China, based on the idea of "Fair Trade instead of War." The new Japanese Government abandons its racist policies and begins to form the economic partnerships with the nascent Chinese Industries that we see today.
According to my Uncle, the pilots of his generation were not all that confidant about fighting the Brits and Americans, although they were led to believe they could defeat them...which they did for awhile.
So? This seems like a pretty astute group. Was this one of those "hindsight is kind of myopic" things, or was it one of those missed opportunities?