The film is based on a novel written by Gulyeoni. The story is about a cheerful high school student named Han Ye-won (Jeong Da-bin). She is a sweet, clumsy and warm girl. On the other side there is Ji Eun-song (Song Seung-heon), a student from vocational school and well-known as a bully. He is hot-tempered and rude but deep inside he is longing to be loved.

One day, clumsily, Ye-won leaves a message on the school website to reply to Eun-song’s impolite message. She is shocked when someone calls her mobile and threatens her. Gradually, her best friend, Lee Kyung-won, tells her who Eun-song is. Eun-song sends Ye-won a message on her mobile: he will wait for her in front of the main gate. She is so scared that she and Kyung-won decide to jump over the school wall. Unfortunately, the moment Ye-won jumps, Eun-song is standing exactly at the other side of wall. She falls on him and accidentally their lips meet. Raising his voice, Eun-song asks for her to take responsibility; she is astonished. His friend explains that Eun-song has never even held hands with a girl. Since she is the first girl to kiss him, as a consequence, she must marry him.

The story continues very fast, at the beginning Ye-won doesn’’t have any feelings for Eun-song, she even rejects his invitation to come to his birthday party. Unknowingly, Eun-song has fallen in love with her; but he is not the kind of guy who knows how to express his inner feelings. He is jealous when Ye-won is approached by other guys but he doesn’’t know how to be with someone he loves.

Although he is rude and bad-tempered, Eun-song always pardons Ye-won’s faults and clumsiness. One thing he couldn’t bear was when he found out that Ye-won went out with Kim Han-sung (Lee Ki-woo), his senior and the one he hates a lot. The broken-hearted Eun-song decides to leave Korea following his mother to the USA. Will Ye-won reunite with Eun-song or accept Han-sung’s love?