For Korea, it would be extremely unlikely, if not impossible. I had addressed some of the issues
earlier within another thread, in which I had stated that Japan actively distorted or destroyed countless Korean sources (beginning in 1925) in order to suit "traditional" Japanese historiography dating back at least to the Edo Period, as well as imposing severe economic and societal pressures (leading to civilian and military resistance for decades). Additionally, the Great Depression (beginning in 1929-30) would still have presumably occurred, eventually facilitating more radical factions to eventually gain power within Japan, and in turn making it likely for assimilation policies to be implemented by the 1930s in order to preempt further disorder within Korea. None of the above could have easily been butterflied away with a PoD in 1918, as the root causes extended long before then.
In any case, it was not 1930 or so that Japanese was heavily promoted within Korea, eventually becoming the sole language of instruction after 1938, and only 20% of Koreans were able to communicate in Japanese by 1940-5, partly due to the relative lack of education (40-60% of children enrolled in elementary school in the same period). Additionally, the name change policy in 1939-40 was forcibly implemented because less than 10% registered voluntarily, and the vast majority of the changes involved registering given names according to the Japanese pronunciation, not changing the Chinese characters as they originally were in Korean (although many family names were changed entirely).
As a result, most Koreans generally identified themselves more with "Korea" than with "Japan" throughout the duration of the colonial period, while assimilation policies were not actively implemented until after 1930-40 or so due to increasing militarization (which may or may not exist in this scenario), although other pressures remained throughout. As a result, once European colonies across Asia and Africa begin to agitate for independence by 1945-70 or so, it will essentially become inevitable for Korea to eventually follow suit.
None of the above means that Japan and Korea can't have relatively warmer ties than that of OTL, though.