Hayate Ayasaki is an unlucky teenager who worked since childhood to make ends meet due to his parents' irresponsible behavior. One day he finds out that his parents were planning to sell his organs to the Yakuza to make money, leaving behind a massive gambling debt on his shoulders. While running away from the debt collectors, he ends up meeting Nagi Sanzen'in, a young girl who is the sole heir of the wealthy Sanzen'in 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 as 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.