This is the story of Woo Yeon, a man who sees his only love as Seung Hee, a girl who believes in falling in love in 3 seconds. It portrays the hardships of first love, spanning 10 years as they mature from children into adults.

Woo Yeon was a high school student who hated studying and spent his days getting into fights. His life appears to be going nowhere until he meets a new transfer student named Seung Hee. He falls in love with her at first sight, though she does not appear to reciprocate. Although Seung Hee doesn't seem interested in Woo Yeon, she grows annoyed at the countless male admirers, and they both agree to pretend to be dating, under the condition that Woo Yeon will stop fighting. He promises, and over time their relationship that was once fake, begins to develop into real love.

However one day, Seung Hee contacts Woo Yeon, telling him to take care. She then leaves town, leaving him heartbroken. He however continues in life, going on to finish high school and find a career. His life seems to be improving, until some time later, he receives a wedding invitation from none other than her, his first love.