One day Haruhi Fujioka searching through the vast campus for a quiet place to study since the libraries are filled with gossiping students, Haruhi finds the technically unused Third Music Room, taken over by the Host Club - a group of six attractive male students who spend their time charming and entertaining the school's girls for profit. During their first meeting, Haruhi is shocked at their behavior which causes an accidental knock over of a very expensive vase valued at ¥8,000,000 (USD $80,000 in the English manga). This causes Haruhi to contract a massive debt with the Host Club. In order to pay off the large sum, Haruhi is employed as the club's "dog" and is constantly ordered to do menial tasks for the members, such as serving food or cleaning up.

Once the club president, Tamaki Suou, sees Haruhi without glasses, Haruhi is promoted to be one of the hosts of the club as a way to pay off the huge debt. One by one, the other club members take notice, until even the club president finally discovers that Haruhi is, in fact, a female, with a self-proclaimed 'low threshold for gender identity', but since she is already accepted by the club's customers and has become one of the main attractions, Haruhi is allowed to remain as a member. She is forced to stay until she has accumulated a total of 100 (later, 1000) customers, at which time her debt would be considered paid in full.