[Yellowscientist]

I was looking into Anarchy in Asia and was surprised to see that of the many Korean nationalist heroes from our textbooks, some were actually anarchists.
Anyway, I have no doubt that Japan had their interests in crushing any resistance in Manchuria, but I fail to see why communists had to crush them too. But there isn't a lot of resources regarding the era, hence the question.

Edit: Some info on the not-well known Shinmin province.

By 1924, the Korean Anarchist Communist Federation (KACF) in China had formed with an explicitly anti-imperialist focus and helped to organize explicitly anarchist labor unions as well. At the same time, anarchist tendencies were developing within Korea itself. For instance the Revolutionists League is recorded to have organized around this time and to have maintained extensive communications with the Black Youth League in Tokyo. By 1929, their activity had materialized fully in Korea itself, primarily around the urban centers of Seoul, Pyonyang and Taegu. The apex of Korean anarchism however came later that same year outside the actual borders of the country, in Manchuria. Over two million Korean immigrants lived within Manchuria at the time when the KACF declared the Shinmin province autonomous and under the administration of the Korean People’s Association. The decentralized, federative structure the association adopted consisted of village councils, district councils and area councils, all of which operated in a cooperative manner to deal with agriculture, education, finance and other vital issues. KACF sections in China, Korea, Japan and elsewhere devoted all their energies towards the success of the Shinmin Rebellion, most of them actually relocating there. Dealing simultaneously with Stalinist Russia’s attempts to overthrow the Shinmin autonomous region and Japan’s imperialist attempts to claim the region for itself, Korean anarchists by 1931 had been crushed (MacSimion, 1991).

Throughout East Asia, anarchists demonstrated a strong commitment to internationalism, supporting each other and reinforcing each other’s movements rather than thinking simply in terms of their own nation-states. The "nationalism" of Chinese and Korean anarchists can thus be seen as a form of anarchist internationalism dressed up in nationalist clothing for political convenience. In both of these countries, the anarchist movement sought to reinforce nationalist struggles insofar as they cast off imperial domination; but they were decidedly internationalist in that the long term goal was to abolish both the Chinese and Korean nation-state systems as well. The same can be said for Japanese anarchists who lent their solidarity to the anti-imperialist movements in Japan, Korea and other parts of East Asia. As noted earlier, the rise of the Eastern Anarchist Federation and its paper "The East" (Dong Bang) is testament to the global nature and focus of anarchism during the early 20th century.

[fuser]

Well I don't know much about this particular anarchist movement/organization but speaking from Soviet experience, the problem with anarchists is that after revolution ("during", they are a great ally) they refuse to accept the sovereignty of Worker's state too and that is of course problematic for the communist party leading that revolutionary workers state.

Hence the crushing.

[Goldberk]

they refuse to accept the sovereignty of Worker's state too and that is of course problematic for the communist party leading that revolutionary workers state.

Instead they accept the sovereignty of the workers, a position the new ruling class of the workers state cannot accept.