Rugby Union has existed for a long time in Korea and they have occasionally beaten Japan. (wikipedia link)
Not much is known about the structure of rugby in South Korea. The information that I am providing is based on some conversations I had with some South Koreans so I hope that is is correct! If anything is incorrect please leave a reply or contact me.
The expat teams are not registered into the KRU or KOC system, their is no direct link.
There are a few teams in elementary school system, middle school and high school. After high school there are 4 main universities that play rugby. 3 of the universities select 10 players a year from high school and the other university only selects 5. So if a high school player doesn’t get selected into one of these four universities it is the end of their rugby career. So on average of the 450 high school graduates who play rugby only 35 get selected into university.
So in short lots of players do not play beyond High School in Korea 🙁