描述行动通讯尚未普及的2003年，一对分隔两地、生活没有梦想与目标的年轻男女，偶然透过一封信给彼此带来安慰与成长，并约定在下雨的12月31日见面的感性青春故事。
Kang Ha-neul
Young-ho
Chun Woo-hee
So-hee
Kang So-ra
Soo-jin
Lee Seol
So-yeon
Lim Ju-hwan
Young-hwan
Lee Hang-na
Mother
Lee Yang-hee
Father
Park Se-hyun
Student
Lee Ye-hwan
Cram School Student
Kim Sung-kyun
Teacher
Ko Gun-han
Jong-guk
Nam Hyeon-woo
Kim Min-seo
Kang Young-suk
Book Worm
