Japanese propaganda portrayed the Japanese military as liberators who wanted save other Asian countries from Western Imperialism. In reality they just wanted to create several puppet governments loyals to the Japanese Empire.
But in a scenario where Japan really did try to liberate Asia from Western and Asian Imperialism, how would they be viewed today? Would the Allies be seen as the 'bad guys' in the Pacific War?
And how early of a POD would be needed to get a Japan that was more interested in liberation than conquest?
First of all, no country will go out of its way to "liberate" another country, especially if it has to go to war to do it, without gaining for itself as well. It will not do things to benefit the locals if it doesn't see a benefit for itself as well.
There is also the problem that if Japan fights against an alliance of Western powers or even makes a mortal enemy out of the USA like it did in OTL WW2, it won't be able to win.
But that does not totally invalidate your scenario. It is not impossible to create a Japan that is friendly with the Asian mainland and acts as a counterforce to Western encroachment. In fact the general opinion among the Japanese leadership in the later 1800s and early 1900s was that if they did not stop the Europeans from expanding in Asia, Japan would eventually be cornered and colonized as well. This was one of the reasoning behind them annexing Korea and later Manchuria, though of course there was also a great deal of greed involved.
The annexation of Korea was obviously not a liberation, so it is certainly not something we want TTL's Japan to do. To stop this from happening we can change the way another power acts. Russia is a convenient one because it is already interested in Korea and prior to 1904 had some presence there. If we can get Russia to be more aggressive, perhaps they try to occupy Korea first. They spend some time building up more infrastructure in the Far East, and attack Korea. They make some gains and start to encounter geurilla resistance. Japan enters the war too. The Russian fleet is defeated. The Japanese, together with Koreans, fight the Russians as allies. Russia is kicked out of Korea. Korea is naturally grateful and enters an anti-Russia alliance with Japan.
So now Japan has "liberated" one country, Korea, which will start modernizing in a manner similar to itself. Japan maintains some troops on the peninsula but they are seen as protectors and not occupiers, and the Koreans have political independence. But China is still in danger and Manchuria is under Russian occupation. The Qing has either collapsed or on its last legs; in any case, there is activity in China.
For conveniences' sake, let's say Qing China is already collapsing by the time the Japanese-Korean alliance has been set up. The Qing are still there, but only in a semi-legitimate form and as a Russian puppet, similar to how the Japanese used Pu Yi in OTL. The Han Chinese hate the rump Qing in Manchuria, who they rightfully see as being controlled by Russians, and are rebelling against the dynasty's authority. But the rebels who are fighting against the loyalist armies are unorganized and ill-equipped. The Japanese see this and are worried. They do not want the Qing to survive because otherwise it will be the same as Russia having influence on all or a lot of China. They want the rebels to survive and replace the old dynasty, so they pick a group and begin to fund it. They send advisers to help train and organize the Han rebels. This is difficult to do and is fraught with problems (such as which groups and leaders to support exactly), but it is seen as politically and strategically imperative to counter Japan's arch-enemy Russia.
After years or even decades of warfare the Qing have been defeated, but China is still a mess, with a weak central government friendly to Japan, but does not control all the provinces and has to make use of warlords nominally loyal to it to keep the country in one piece. The Russian threat probably still exists to some degree depending on how well the Tsar has been doing in Europe and Central Asia. China is not doing that great but at least it has been "liberated" with the help of Japan, which is doing lots of developmental business in Chinese cities. Perhaps Japanese companies are outsourcing jobs to cheap Chinese labor. In any case Japan is still doing okay.
By the late 20s/early 30s, Japanese society is not as militaristic as it was IOTL, because its experiences ITTL have shown the people and leaders that it does not have to directly control the Asian countries around it in order to have them modernize and ward off European expansion. Japan can benefit economically from a big European war, and it can also do trade with the industrial countries in peacetime. Diplomatically, Japan will be enemies with Russia and perhaps other Western powers, but it would be stupid to be the enemy of all of them. Japan might thus find partners in Germany (few or no colonies in the East) and the USA (far away, not dependent on colonies for its prosperity). The USA in particular is interested in an "Open China", and if Japan shall oblige, everyone is happy.
Over time, Japan will still champion decolonization in South Asia, but as it has been given some breathing room in the form of friendly and independent China and Korea, it will not find it so imperative to actually help the Indonesians or the Indians, who are still under colonial rule, and it turns a blind eye to the Philippines which is controlled by the USA. The chief enemies of Japan will be Russia, France, and Great Britain. It may fight wars with these powers in SE Asia, and have a say in the fate of the relevant colonies as they become independent. If there is a Cold War of some kind, Japan could be seen as a third side or nonaligned bloc.