Hayate Ayasaki, a down-on-his-luck high schooler, works tirelessly to support his spendthrift parents. When they vanish, leaving him with a staggering debt of 150 million yen, Hayate's escape from relentless debt collectors leads him to a fateful encounter. Mistakenly attempting to abduct a girl, he instead becomes her accidental hero, sparking a romance. This girl, Nagi Sanzenin, turns out to be the heiress of a wealthy family. Grateful for Hayate's gallant act, she appoints him as her butler and settles his debts. Thus, Hayate embarks on a new life as a combat butler, devoted to safeguarding his young mistress through perilous adventures.