I wonder how much it comes from the culture in Korea. I've been living in Tokyo for 3 years, and although I never to the university here, I my observations in the country are that: * Korean people tend to stick together and don't mix much with other nationalities * Chinese people integrate so well that their Japanese friends and acquaintances barely notice they are not Japanese. And as they are not afraid to speak in English they're able to make English speaking friends too. * Unless they had some exposure to western countries, many Japanese people tend to be superficially friendly due to keeping their public persona separated from their true feelings (the 2 concepts of tatemae vs honne). And this not specific to making international friends, as they have themselves the same difficulty making Japanese true friends. * English speaking foreigners tend to hang out together or with English speaking Japanese people, unless they're introduced through a friend to Japanese people who can't speak English.