Hayate Ayasaki is a sixteen-year old boy who has been working hard earning money as a bicycle delivery boy. He loses his job after his employer finds out he is still in high school, and his irresponsible parents spend the money he had earned. Hayate tries to kidnap a young girl named Nagi Sanzenin, but fails in his attempt. Later, Hayate saves her from other kidnappers and Nagi repays him by offering him a job as her new butler. However, overcome by injuries received during the rescue, Hayate collapses and is taken from the scene by Nagi's private helicopter.

Awakening within Nagi's mansion, Hayate incorrectly concludes that he has died and gone to heaven, and resolves to make the most of it. While he is enjoying a soak in an enormous indoor bath, the water re-opens his wounds and he passes out. When he regains consciousness, Nagi and Maria explain that he is Nagi's new butler. Eager to demonstrate his aptitude for the job, Hayate begins cleaing the mansion at a remarkable rate, drawing on cleaning skills he gained during previous employment. He finds a manga that Nagi has been drawing, and when he mistakenly refers to it as a picture diary, Nagi ejects him from the room. Believing himself fired, Hayate leaves the mansion and is immediately abducted by the loan sharks that are after him. All seems lost until Nagi, wearing an unconvicing disguise, appears and rescues him by paying off his debt. Hayate will now work as Nagi's butler to repay her.

Hayate wakes up Nagi one morning to find a large white tiger sleeping with her in her bed. The tiger, named Tama, nabs Hayate and carries him outside to fight. Hayate inevitably loses. Afterwards, Klaus, who is still upset about Hayate being Nagi's butler, challenges Hayate to a match with a robot to see if he has the necessary skills to be a butler.

When Nagi goes to school, she forgets to bring her lunch and Hayate offers to bring it to her. Once he gets to school, he is stopped at the front gates by a teacher (Yukiji) who thinks he is an intruder. Hayate eventually gets into the school, but the teacher continues her pursuit. Once inside, Hayate meets the student council president of the school, Hinagiku Katsura, for the first time, and helps her down from the tree she was climbing. As a reward, she brings him to the top of the Student Council tower so that he could see from the terrace. Yukiji, who is still searching for Hayate, finally finds him there and ends up fighting Hinagiku. After taking Nagi's bento box from Hayate, she jumps onto the railing of the terrace only to get blown off by a breeze. Hayate promptly rescues her, which ended her hostility to him. In the process, however, she had thrown Nagi's bento box onto to ground and spilled its contents.

Nagi does not want to go to school today and instead stays home to hang out with some friends. One of her friends, Sakuya Aizawa, arrives and starts to teach Hayate to be a better comedian despite Nagi insisting that he is a butler. Hayate later goes out to pick up some more tea wearing a cashmere coat, but finds the journey perilous.

Continuing from the last episode, Isumi gets to Nagi's mansion but Hayate leaves to pick up the tea that he was supposed to get. Hayate is ambushed by Isumi's protective staff and the loan sharks from the first two episodes. Hayate eventually makes it back, but comes down with a cold. The next day after Hayate has healed, he meets a young boy and his maid who have come to Nagi's mansion. The boy, Wataru Tachibana, is Nagi's fiancé.

Wataru, who is infatuated with Isumi, challenges Hayate, whom he perceives as a rival, to a duel. Hayate loses to Wataru on purpose, hoping for a romantic conclusion between Wataru and Isumi that will allow Nagi to break off her unwanted engagement. However, his overly obvious act ends up hurting Wataru's feelings. In order to reach Wataru and apologize, Hayate, together with Isumi and Nagi, must brave the Tokyo subway system.

Nagi gets Hayate to first try on a female school uniform, much to his displeasure and before he can do anything about it, Maria comes to Nagi's room and sees what is going on. Nagi and Maria then proceed to put Hayate in a full cat-girl outfit which entices Tama's animal instincts. Afterwards, Hayate runs into Klaus and initially tries to run away, but in the end Klaus' instincts take heed, and Maria must interfere. Later, Hayate and Maria play a game of pool where if Hayate loses, his debt will increase to 200 million yen.

Hayate tries to motivate Nagi to go to school finally, and offers to take her to and from school everyday from now on. Nagi reluctantly agrees and goes to school for the day, but when she comes back it turns out she forgot her notebook at school. Hayate offers to go to school late at night to bring it back and at the school gate he runs into one of the school's teachers he met earlier.

This episode, which is anime-only, takes place during the same time as episode eight and shows some other strange things that were going on in the background. A demon living inside an old video game is awoken and takes three of the student council members from Nagi's school inside the game where they must defeat her to return to the real world. Hinagiku, the student council president, arrives soon after and they go to destroy the demon, but she ends up ending it herself.

Nagi, with Hayate, Maria, and Sakuya, go to visit the head of the Sanzenin family — Mikado Sanzenin. Hayate runs into him outside, but initially believes him to be a landscaper on Mikado's estate. After Mikado reveals himself, he informs Hayate that his life is infinitely worthless while he is living to merely pay off the debt he owes Nagi. Mikado gives him a special pendant before leaving. Later, Hayate decides that he will protect Nagi from anyone that tries to hurt her, which greatly flusters Nagi.

After waking up from a dream about his childhood, Hayate talks with Maria about having dreams to live for and believes that dreams in life are very important. After revealing a childhood dream of his, Hayate gets the day off and decides to visit his old high school. There, he meets one of his old classmates, Ayumu Nishizawa, who has a crush on him. Hayate finds out that his parents took the rest of his tuition money, leaving him without a high school to go back too. After he begins to leave, Ayumu confesses her love for him, but he turns her down. Later, Ayumu gets taken into the ground of Nagi's mansion under the pretense that Hayate was being held captive by yakuza.

After turning down Ayumu, Hayate continues to wonder what she is doing while at he is at the mansion. Transfer documents arrive in the mail for Hayate to transfer into Nagi's school, and Hayate is overcome with joy to the point of crying. Hayate attempts to study the rest of the day for the exam the next day, but continuously gets interrupted by Klaus and Tama, so he does not get much sleep. The following day, Yukiji Katsura, one of the teachers at Nagi's school, has a bit of fun at Hayate's expense in order to "loosen him up" before the real exam. However, due to the physical and mental exhaustion he acquires as a result, he fails the entrance exam by one point. Yukiji is told that she must go to the Sanzenin mansion to inform Hayate, but is hesitant to do so because she believes herself to be the reason Hayate failed.

Hayate and Nagi are excited about Hayate being qualified for Nagi's school. However, Yukiji Katsura struggles to tell Hayate that he actually failed and that she was the indirect cause, having played pranks on him before the exam. She continually gets beaten by her little sister for skirting around the issue. Hayate eventually finds out and is disappointed but finds out that he actually qualified thanks to a recommendation from Maria.

Hayate goes to school early with Nagi despite her complaints. They meet a butler with a student along the way who eventually runs off with Hayate's necktie which makes Hayate and Nagi fetch a new one from home. Hayate has various discussions with Nagi and discovers that she jumped a few grades and thus is a high schooler despite her age. Hayate also discovers that Nagi used to be in a kendo club with Hinagiku but quit. Hayate decides to put Nagi back into the club when he is challenged by someone in the club.

Hayate is ready to fight. However, the boy who challenged him calls his butler to fight instead. The butler then punished the challenger for being a coward. Hinagiku then stops them and the battle starts. Hayate stands no chance against the butler since he lacks a last-minute powerful move. However, he eventually wins by using the boy who challenged him as shield calling it the "Art of Changing Bodies."

Nagi tries to gain experience after her work was rejected by a manga magazine. She believes she has no experience being lazy and staying in all the time, despite being rich and thus not having any problems living. She asks Hayate who has extraordinary experiences, but then becomes angry when Hayate tells her he once won a 'Manga Newbie Award'. She continues to gain experience while attempting to clean the house (which she messes up terribly) and by trying to serve food.

The students at Hakuō Academy go to a remote island for beach class. The butler of the beach resort named Schmidt hen Bach greets them and tries to create fun experiences for the group. However, the group of students is not having fun and want to go home, but Schmidt is not willing to let them go.

Wataru notices that Saki is acting strange so he decides to ask Hayate and Maria for help while he's picking up the cursed video that Nagi rented. It seems that Wataru forgot about Saki's seijin shiki and the people who watches the cursed video will be attacked by a giant cockroach. While Wataru is asking Nagi where he could buy a present, Hayate and Maria battle the giant cockroach. Nagi mistakes Wataru's present to be for Isumi so she sends Isumi to Wataru's house.

Hayate is searching for an ultimate attack and Maria suggests looking in the Sanzen'in library for hints. They find a book that teaches the Sanzen'in secret ultimate attack. After some training, Nagi finds out that Hayate is training for Hinagiku's sake and burns the book. Depressed, Nagi leaves the house at night where she meets Ayumu Nishizawa who challenges Nagi.

Nagi decides to take Hayate to an amusement park in her own backyard. While Hayate is roaming through the haunted house, Robot Eight, who was defeated in episode 3, appears to get revenge. After Eight's plan fails, he flees, upgrades, and breaks into Nagi's mansion for another chance for revenge.

With summer vacation coming to an end, Nagi is saddened that there won't be anymore free time to spend with Hayate. After reading a manga, Nagi decides to take Hayate fishing. While Hayate and Nagi are having a romantic time fishing (in Nagi's mind), the lord of the lake overturns their boat. Returning home, Hayate takes a bath and is joined by Tama who breaks the bath's water heater. Hayate becomes depressed because he believes he's always causing problems for Maria and attempts to fix the bath, only for it to be destroyed once again by Tama.

Shiori Makimura is sent to take over Yukiji Katsura's homeroom at Hakuō Academy after a number of failed projects at M.H.E. Corp. Yukiji Katsura is demoted to sub-homeroom teacher. In order to get her old job back, Yukiji begs Hayate to help her blackmail Shiori. Hayate refuses, but Shiori runs away crying and calls Eight after Yukiji manages to get a picture of Hayate on top of Shiori after he falls down.

Hayate is having a bad day thanks to the pendant that Nagi's grandfather gave to him. After Hayate and Wataru rescue Isumi's stole, Isumi thanks Hayate by decursing the pendant. Nagi and Wataru become depressed because they misunderstand the decursing as an act of love because they embraced. Nagi runs away from home to Wataru's video store.

Nagi is despondent over her conflict with Hayate, so she, Saki and Gilbert plan a fake kidnapping in Isumi's house underground. However, things turn bad when a Mecha programmed by Shiori goes crazy, and it is up to Hayate to go rescue Nagi and to recover his butler's status.

Hayate is running an errand for Nagi and meets Ayumu in the park. Still embarrassed about their last encounter, Hayate pretends he has amnesia and is unable to get out of the mess after Ayumu claims he is her butler. Nagi claims Hayate back and gets him to reenact experiences he faced in Nagi's mansion to recover his memory (even though he didn't lose them).

The superintendent of Hakuo Academy, decides to hold a Butler Battle Tournament to see who the strongest butler of all Hakuo is. At first, Hayate is reluctant to enter, but Nagi convinces him to do so so she can see him win. In the meantime, Hinagiku becomes a temporary butler so that she can enter the tournament to interfere with the superintendent's plans.

Hayate defeats Klaus and Tama by catching Klaus' ribbon when falling off during Klaus' Ultimate Move, leaving the whole public under the impression that he has the power to defeat opponents without even touching them. After numerous retirements from Hayate's opponents and battles through the tournament, Hayate defeats Hinagiku in the finals and fights Shion. After defeating her by discovering her weak point, the Superintendent vows to bring Hayate to her by calling her Dark Butlers League.

Saki's mother asks Saki to have a marriage meeting. Wataru becomes worried and asks Nagi on what to do. They decide to go on a marriage meeting tour to spy on Saki. The man Saki is to meet turns out to be Kyonosuke Kaoru, but they both reveal that they both have someone else they like. After a misunderstanding, Wataru decides to crash the meeting by sending Tama to kidnap Kyonosuke and to lose to Wataru on purpose. The plan is set back and Yukiji kidnaps Kyonsuke instead. In the meantime, Kirika sends Duel Butler to bring Hayate into the Dark Butlers League.

Yukiji is found murdered at a hot spring inn and Detective Nagi decides to take it upon herself to solve the mystery. After a number of wrong assumptions, Nagi blames the voice in the sky ("Ten no Koe", i.e. the narrator). Kirika sends another butler to defeat Hayate, and they have a B-Daman battle.

Sakuya visits Nagi. Nagi becomes offended when Sakuya tells her she's a brat because she has no siblings and claims she can be a better sister than Sakuya. Nagi orders Hayate to find kids that are lost on her property so she can prove it to Sakuya. Hayate comes back with Itsuki and Shunji, and Nagi plays with them while her SP looks for their parents. Sakuya suspects the kids to be thieves and catches them in the act. Afterwards, Kirika sends the third mysterious butler, Mini Yon, and he challenges Hayate to a Mini 4WD race.

Isumi is planning to come to Nagi's house but she ends up getting lost again. Fortunately for her, Sakuya finds her, but along the way, they find a man with the head of a carp who begs for their help. The carp man asks Isumi to phantom bust phantoms who are tampering with his lake.

It's culture festival time and Hayate is kept busy by the students and teachers. Nagi searches for him, but she is unable to find him. A mysterious dark butler tricks Nagi and hypnotizes her. In her hypnotic state, she finds Hayate and leads him to the mysterious dark butler.

Nagi, still in her hypnotic state, helps organize the second day of the school festival with the help of Superintendent Kirika. They organize their own Comiket where Nagi sells her own dōjinshi. Kirika challenges Hinagiku to see if Nagi's dōjinshi or Hayate's butler cafe can make the most money. When Nagi tastes the cake that Hayate made for the competition, her hypnotic state goes away.

Nagi is having trouble writing a new manga, so she orders Hayate to go out and gather references for her. She also gives Maria and Klaus the day off because she feels she needs to be alone to concentrate. Maria tags along with Hayate and the two soon become uncomfortable because their joint effort to gather references feels like a date. Yukiji, Risa, Miki, and Izumi spot them and try to get the two to kiss by bringing them to the trendiest date spots. At the end of the day, Nagi shows Hayate her fiery wrath when he shows her the photo references he took, which are mostly pictures of him and Maria having fun together.

Klaus is feeling depressed after Nagi gives him permission to retire after he tells her about a dream he had, where he retired on a coffee plantation in Brazil. After Maria tries to convince Klaus to stay, Klaus decides to challenge Hayate to see who is the better butler. Klaus fails at this and has his mind set on retiring. Maria comes up with a plan that involves Hayate's female alter ego, Hermione. This plan fails as well and just before Klaus is about to leave, Nagi thinks of a way to make Klaus stay. Her plan succeeds and Klaus decides to stay as a Sanzen'in butler.

Nagi asks Hayate what type of girl he likes, after reading a romance magazine which states that Nagi's zodiac sign, Sagittarius, will face a crisis in terms of romance. Hayate tells her that he likes girls that are normal and makes a passing remark that Nagi "wouldn't understand". Nagi runs off in rage, determined to learn how to be 'normal'. Nagi meets Ayumu Nishizawa and comes to the conclusion that tagging along with her will help her learn how to be 'normal'. After a day of following (and bothering) Ayumu, she invites Nagi to stay at her place. Ayumu gives Hayate a call, at Nagi's request, to inform him that Nagi will be staying over. It turns out that Hayate has been following them. Just as Hayate was about to leave, Isumi calls in distress, trapped at the top of a nearby tower. Wataru rushes to save her before Hayate, but it was ultimately Hayate who did most of the work.

Nagi, Hayate, and Maria go to a Christmas party hosted by Nagi's grandfather. Just like the previous Christmas party, Nagi escapes - this time with Hayate. They head to the park where Nagi tries to make romantic advances on Hayate, but they are interrupted by a mysterious dark butler, Cyborg Butler, and Superintendent Kirika. Hayate is defeated, but they are saved by Himegami, who now calls himself Princess God. The next day, Hayate fails at all his butler chores and Himegami explains it is because Superintendent Kirika drained all his butler powers. In order to keep Nagi safe, Hayate resigns as Nagi's butler and leaves the mansion.

Kirika asks Hayate to wear the ancient butler robe which has been rejecting countless butlers. In exchange, she promises to leave Nagi and her fortune alone. Nagi, Hinagiku, and Himegami come to Hayate's rescue, but they arrive too late, as Hayate has turned into a nekomimi maid. They battle Kirika and Shion and during the battle, Nagi's pleas reach Hayate. The nekomimi maid uniform transforms into the legendary butler uniform. With his newfound power, Hayate defeats Kirika's snake, Jörmungandr.

On the night before New Years, Nagi orders Hayate to bring her to Kujukuri Beach to have a romantic date watching the sunrise after reading about it in a manga. Hayate is forced to take her on a bike since he is not old enough to drive. He manages to make it on time, but Nagi falls asleep just before the sunrise. The next day, the mansion's circuit breaker overloads and Hayate goes to the annex to turn it back on. On the way there, he gets stuck in a blizzard which is really caused by Sakuya's snowblower. He manages to turn the power back on, but passes out due to the extreme cold. After insulting Sakuya without meaning to, she (and her bodyguards) ditch him and leave him on a stretcher in the annex.