There is even a Greek Orthodox Diocese in Korea which has a number of Korean Orthodox priests and eight parishes in the country. I visited their Cathedral in Seoul for Vespers. There were a large number of Koreans present along with some Russians. You can always tell the Russian Orthodox apart as they never sit in church and bow and prostrate themselves frequently. The Orthodox Diocese is under the care of two Greek bishops who are capable of, as I can attest, fluently chanting in Korean!
Christianity came to Korea as a liberator, not an oppressor. The idea that all people are equal in the eyes of God was revolutionary to many and immensly attractive in a society which was very hierarchical and very much segregated by class. One of my theology professors, a man who spent much time in Nigeria in the missions there, often told me that people need to see the Good News of the Gospel of Christ as truly good and truly new. That happened here.And while you're learning about Christianity in Korea, check out a couple of videos from the Korean Orthodox Church: