park jongseong, park jina's bestfriend who she calls with 'jjongsaeng'. they're roommates who are the same age and are mostly known as 'bestfriends' in campus by everyone they know. most people call him jay

jay knocks on jina's bedroom door and opened it, standing by the door while speaking

"jin, you comin to heeseung's party tonight?"

he asked, crossing his arms while fixing his glasses a bit