Hayate Ayasaki is an unlucky teenager who has worked since childhood to make ends meet due to his parents' irresponsible behavior. One day on Christmas Eve, he finds out that his parents shoulder him with a massive ¥156,804,000 gambling debt, the Yakuza (who the money was borrowed from in the first place) plan to settle that debt by selling his organs on the black market. While running away from the debt collectors he ends up meeting Nagi Sanzenin, a young girl who is the sole heir of the wealthy Sanzenin estate, and due to a misunderstanding, Nagi ends up falling in love with Hayate. After he rescues Nagi from some kidnappers, she hires Hayate as her new butler.
Aside from performing his ordinary duties as a butler, Hayate must fight to protect Nagi from harm, a difficult task since her life is always in danger because she is the target of other individuals coveting her family's fortune, and sometimes deal with some extravagant requests from her, oblivious to Nagi's true feelings for him. In the later story, Hayate has to deal with the feelings of several other girls, Ayumu Nishizawa; his former classmate who harbors a crush on him, and Hinagiku Katsura; the student council president of Hakuō Academy who ends up growing attached to him. Hayate had a romantic relationship with a childhood friend, Athena Tennousu, who is chairwoman of the board of Hakuō Academy.
Due to a series of events involving Hayate, Nagi, and Athena during Golden Week, Nagi ends up forfeiting her inheritance. With the last of her savings, Nagi moves with Hayate and her maid Maria to an old apartment building called "Violet Mansion" owned by her late mother, Yukariko, and rents its extra rooms for income: having Chiharu Harukaze; the secretary of Hakuō Academy, Hinagiku, Athena (in child-form), Kayura Tsurugino; an "elite otaku", Ruka Suirenji; a "singing idol" who develops feelings for Hayate, and Ayumu, as its tenants.
