I recommend reading Carter J. Eckert, Park Chung Hee and Modern Korea: The Roots of Militarism 1866-1945 (Harvard University Press, 2016), pages 5, 73-86
The Korean collaborationist officers in the Japanese forces was neither a small group nor isolated from mainstream Korean society. The Korean officers in the Japanese forces were not simply mercenary quislings as they had to be nominated. Colonial Korean schools dutifully carried out their assignment to nominate large numbers of their best and brightest students to become officer cadets. Commissioned officers were highly respected in 1930s Korean society, who treated them with pride as heroes within the local community. Of the 2nd batch of top students in the Manchurian Military Academy who were considered good enough to join the Japanese Military Academy in Tokyo, half were Koreans (including future President Park Chung Hee). Indeed, the influence of pro-Japanese elements grew even larger after WW2. ROK Military Academy superintendent and later Minister of Defence Chong Naehyok was also a graduate of the JMA, and he made sure that South Koreans were trained according to the same mould. According to interviews decades after the war, the Japanese officers who had graduated from the Academy with Park Chung Hee felt that the IJA spirit was still preserved in the ROK army.
