Yi Hyun has a childhood friend named Kim Hyung Jun. Back then, she had a great crush on him, but one day Hyung Jun just disappeared, and that was nine years ago. She thought their love story just ended right after he left. She believed that a happy ending with him was impossible to happen at all. Upon forgetting his feelings for her one great crush that turned to a one great love, she still fails. She knew who her heart longs to be with. She wanted Kim Hyung back in her life. 

Once again, after nine long years of desperately holding on, the guy she has been waiting almost half of her life, finally comes back. Now that she feels happy, her only wish this time is to end their story with a happy ending. That's why she writes her love story with a title, "Happy Ending."