The Characters:

Im Yoona - born from a middle class family, not too poor but not to rich either. She is a hard worker whose studying to be a nurse since she wants to help her family and also achieve her dad's dream of becoming one. She is the only child and lives with her mother and grandpa. Although she is a cheerful person, She meets Oh Sehun who turns her life upside down.

Oh Sehun - born from a rich family. He is a grandma's boy and because Of this he is a sweet and caring person unlike his brother who always play around with girls. he is a workaholic because his family entrusted him with their company. out of his 2 siblings he is probably the most capable one to manage their business since their family owns one of biggest company in Korea, he is a very serious person specially when it comes to his work. He meets Im Yoona who changed the way he viewed life.

Oh Jong In or Kai - he is the youngest out of the Oh siblings. he is a playboy who always goes to the bars/clubs and sleep with girls for fun, but when two people unexpectedly came in his life he starts to realized that love can come in an unexpected way.

Byun Taeyeon - the oldest out the the Oh siblings. She is married to Byun Baekhyun. She becomes friends with Yoona when she helped her and her bestfriend Tiffany escape from her abusive husband.

Naynay (Granny) - she is the grandma of the Oh siblings. She's got a secret that only she knows, until Kai found out about it and helped her hide that secret from everyone.
Pronounced as nai nai

Note: the other characters you will get to know as the story progresses. I will add them in the list when I introduce them.