Fujioka Haruhi is a schloarship student of the Ouran High School, one day from a lower-middle class family who tends to have a low threshold for gender identity. the male student's uniform. Because of this and the high cost of the school uniform, Haruhi wears long slacks polo shirts that resembles the male student's uniform. Therefore she is being known as a male student, one day when Haruhi is looking for a quiet place to study, she come upons the Third Music Room, where she found the Ouran High School Host Club - a group of six attractive male students who spend their time to provide hospitality to female and gaining profit from them.

Haruhi is shocked at their behavior when they first meet, which causes her to accidentally knock over an expensive vase valued at 8,000,000 Yen. This causes Haruhi to contract a massive debt with the Host Club. In order to pay off the large sum, she is employed as the club's "dog" and is constantly ordered to do menial tasks for the members, such as serving commoner's food or cleaning up.

Eventually, Haruhi is promoted to be one of the hosts of the club as a way to pay off her debt. The other club members soon discover that Haruhi is a female (with the president Tamaki to understand this last), but since she is already accepted by the club's customers and even became one of the main attractions of the club, Haruhi is forced to stay until she has accumulated a total of 1,000 customers, when her debt would be considered paid in full.