Yoo Ah-Ara 

a beautiful girl who started seeing ghosts when she was 17 , being scared and alone made her turn into a cold person who is just waiting for his life to end , but what if someone actually saved her from the hole she is falling in ?
After an accident she finds out she have a heart condition which isn't very good.
 

kim jongin ((kai))

a lost soul or a ghost who finds out that yoo ah ara can see , hear , feel him . 
very sweet , kind , dumb .

Yoo Yoon-Jae

yoo ara's brother but they were separated because of there parents when they thought that yoo ara is bad for him, really loves and every once in a while he tries to sneak to her and stay with her for a while until he have to get back .

kim junmoon ((suho))

 
yoon ara's doctor and best friend who is more like a brother , they treat each other like a family and he knows about yoo ah ara's ability