The only 'plausible' way for Imperial Japan to retain/gain an Asian Empire is if the Anglo-Japanese Allience and Anglo-Japanese relations stay intact/deepen into a closesr frienship throughout the 1920s, this means that during the lead up to WWII Japan sees it's place to stand by the Allies against the events in Europe.
Part of the above would presume that Imperial Japan never really goes 'milliterist' during the 1930s economic problems. Ergo, we might have to butterfly away this bust in the US, or have Imperial Japan rely a little less on foreign investment capital in this era.
In such a case the Sino-Japanese co-operation movements from the 1920s may deepen, entrenching the notion of Sino-Japanese co-operation against threats to both sercurity. Thus the Japanese play on the Nanking incident to impress upon the Chinese a need for unity, while also allowing the British special concessions.
In principe by the 1930s, the bugbear becomes the Communists. What happens if the Japanese uni-laterally decide that they support the Chinese nationalists and decide to intervine against the Communists, simulatainously supporting/legitermising the Kuomintang Government, but also supporting regional independance by graining Japanese gurantees for the various warlords/provinces of China?
The Kuomintang Government, thus gets shoehorned back to its founding roots as the notion of a 'federal entity', which perhaps the Japanese play on during the late 1920s and so sets the seeds to allow the partitioning of China along regional lines. Thus via the mid/late 1930s proposes a form of 'union of asian states'.
This becomes the grounding for a Co-prosperity sphere, that is aligned against Communism, and nominally with the Anglosphere Allies.
In such a history, Imperial Japan may never fight anyone in the WWII years, but being able to power play the colonial regimes in the DEI, Phillippines and Indochina to this notion of an 'asian sphere' might be able to get a regional support going for this 'new east'.
As the world moves into the Cold War era, the 'Asian Prosperity Sphere' might develop as a 3rd power bloc, weaker than the Allies and Soviets, but nominally aligned to the former against the latter, but strained over colonial holdings.
In the longer run, the Chinese and Japanese economic explosions may have them outlast the Soviets and today the Cold War between the 'East and West' might still be there in the background.