I found it. It is the song "Only Our World" ( ), which is included in "Zzang O.S.T" (?). But it’s a pity that it’s been so long ago that even big sites like South Korea’s NAVER Music don’t have sound sources to listen to.

Korean lyrics:

1. ...? ? ..

..? ?.

? ? ..< /p>

...? . ? ?.. ? ? ?..

~

2. ? ? ..

.. .? .. ? ? ? ?.. ? ?

...