IMHO, it's no more impossible than a Neutral USA. The simplest way to bring about the outcome requested by the OP though, with a tripolar world in which Japan doesn't have to fight the US, but gets to keep Manchuria, would be for the Germans to exclude Japan from the Axis, in favor of KMT China. As such, the Empire of Japan ends up becoming a nominal partner of the Allies, in much the same manner that the Soviets were IOTL; and its Co-Prosperity Sphere (encompassing its occupied territories and friendly regimes- probably the majority of the Asian nations which break away from colonial rule, in the 'Yellow Tide' of Asian decolonialism, akin to the 'Red Tide' of Soviet Republics in Eastern Europe and Central Asia) ends up becoming a third side in the Cold War. Japan wouldn't be neutral, strictly speaking- but it's the best way to bring about the scenario which the OP wanted.