Three boys are desperately struggling to "make" a girlfriend in their sad, adolescent lives. They then realize that their classmate, Ghang Han-Gyul—the manly, serious, quiet person of their class—has been secretly going out with a beauty for 100 days*. This triggers the friendship between the manly, serious Han-Gyul and the three dateless losers.
*A 100 day celebration of a relationship is seen as very significant.
(Source: MU)