오랜만이야
Long Time No See 

Lee Soojin and Kim Jongin. They hated each other since they entered middle school together. They're two different souls. Soojin, being the creative and imaginative girl of the school and Kai, being the player and kingka. Two days after a party of Soojin's cousin, Soojin suddenly dissapears. The only thing Soojin left, was her diary and a note to Kai.  

"너 어디 있니?"
"where are you?"

main characters:
lee soojin: has a rather bipolar personality. for some reason, has to flee from one city to another.
kim jongin/kai: big dislike to soojin, but cares deeply for her, is involved.

other characters:
oh sehun: soojin's best friend.
xi luhan: undercover spy and good friend of soojin.
zhang yixing/lay: an old childhood friend of soojin.
kim minseok/xiumin: soojin's cousin, undercover spy.
do kyungsoo: good friend of soojin, works in the same organization as luhan and soojin.
wu yifan/kris: the enemy, leader of p.h.o.e.n.i.x 
kim joonmyun/suho: leader of black pearl.
park chanyeol: same organization as kris and tao.
huang zitao/tao: the maknae of ph.o.e.n.ix, same organization as kris and chanyeol.
byun hyomi: kai's ex-girlfriend.
kim jongdae: the right hand of suho, interested in soojin.

additional info:
p.h.o.e.n.i.x: the enemy organization. has been set up by kris' grandfather. his grandfather wanted the diamond that badly, that he trained a lot of people to get it.
black pearl: the good organization. the uncle of suho has been keeping the diamond since he set up his own organization for safety.
the diamond: or mostly known as osiera r'tear (the actual name of the diamond), is really expensive.

update ; 17/10/2012.
here is a blog post about this story, you can find all kind of information here! {click here}