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.

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.

On the way the school, Hayate and Nagi bump into Hinagiku who is worried about her sister after she gave her New Year's allowance. Yukiji appears, shocking the three with an unusually cheerful attitude, giving Hinagiku a New Year's allowance because of a promise Yukiji made with her 10 year ago (although it was only 500 yen), and shocking them even more after they found a letter of resignation which dropped from Yukiji's bag. When homeroom ends, the class begs Yukiji to stay as a teacher causing Shiori to burst out in tears, who is happy that the class cares for her and decides to not resign. The resignation letter belonged to Shiori who found being Yukiji's superior harder than she thought. Yukiji was happy because she found many signs of good fortune.

Nagi, perplexed by Hayate's apparent lack of weaknesses despite being a main character, plots ways to find chinks in his armor. As her various schemes fail to produce results, Maria, Sakuya, and Isumi get swept up in the flow and discuss their weaknesses as well. Hayate and Wataru begin studying German in preparation for a Hakuō mathematics exam, while Maria tells Hayate a bit of background information on Isumi, Sakuya, and Wataru. When they go to check on Nagi and Wataru, Nagi becomes jealous that they are alone together, prompting Maria to remark that Hayate's weakness seems to be not understanding the female heart.

While working on her manga, Nagi gets the idea that, instead of chasing after Hayate to further their relationship, she must give him the cold shoulder and force him to chase her. A convenient invitation from Sakuya to a cruise on a familiar-looking ship gives her the perfect opportunity to set this plan into motion. As Hayate wanders around amazed, she shuns him over and over, culminating in the command to "explore the ship yourself". The ship is then threatened by a trio of terrorists, who are handily defeated by the Sanzen'in and Aizawa butlers; however, one of them sets off a bomb, blowing a hole in a cargo hold Hayate had just wandered into. There, he meets Isumi, who had become lost, in danger from a pair of large sharks. As the ship-goers are evacuating, Nagi remarks that Hayate hasn't shown up yet, and goes to search for him. She finds him holding off a shark; as she dives into the water to help, she is attacked by the other shark. Hayate defeats the sharks to save Nagi, but falls unconscious from the combination of the cold water and wounds he received from the earlier explosion. He is saved by Klaus, but Klaus' attitude causes Nagi to worry, as it has the effect she was trying to achieve herself.

Nagi completed an improved version of her manga, but still, no one can understand it except for Isumi. She takes Hayate, Maria, Isumi, and Sakuya out for ramen, but they find themselves in a hidden animation studio where they are shocked to hear that Nagi's manga is going to be animated. The directors declare Nagi's demands to be impossible, but they end up animating it anyways because of a rumor that their stock will go up if they do it. After the premiere one week later, everyone is at a loss for words.

Nagi surprises Maria with an overnight relaxation tour at the Hyatt Regency hotel after Maria becomes upset when Nagi and Hayate thought she looks older than her actual age. When Hayate orders for room service, they meet Izumi to find out the students of Hakuō Academy are running the hotel for a one day experience event. Maria enjoys a few of the hotel facilities until the students are unable to accomplish their jobs and ask Maria for help especially when the Kirika and Shion visits. Maria spends the rest of the day helping the students in secret from Nagi and Hayate.

Wataru is shocked one day when he sees that Isumi is wearing a different school's uniform and can even get from one point to another without getting lost. Wataru seeks help from Nagi, and eventually going to the high school he saw Isumi go to earlier. Wataru finds Isumi showing a lot of attention towards the pitcher on the baseball team, which leaves him to jump to conclusions. It turns out Isumi was merely trying to exorcise the spirit of a girl who had liked the pitcher. Wataru challenges the pitcher to a match for Isumi's heart, but loses which greatly depresses him. Isumi succeeds in exorcising the spirit, and thanks Wataru for his help, which relieves Wataru of his worries about Isumi.

Due to Hayate's most recent borderline test scores, Nagi gives him some time off to study. Meanwhile, Klaus sends a robotic butler which looks somewhat like Hayate to fill in for him while he is studying. The robot, known as Thirteen, does an even better job as a butler than Hayate even could, which depresses him when he finds out. Thirteen devises a plan to get Hayate and Nagi alone together, though only Hayate realizes this after the fact. That night, Thirteen goes into space to destroy a meteor heading for Earth, but is stranded on the moon with no power in the process of saving Earth.

Hinagiku's birthday is coming up, and her mother asked her if she would be spending it with someone she liked, which makes her become anxious around Hayate the following morning. Both Hayate and Hinagiku find unsigned love letters addressed to them at school, and they both think that each other might have sent the letter. They later meet the the appointed place in front of the kendo dojo, but find out that it was Kōtarō Ayumamiya who sent the letters in order to show Hinagiku that he could defeat Hayate. Hinagiku then leaves, mad at Hayate for saying that she wouldn't do anything girly and lying that he didn't expect the person who wrote the letter to be Hinagiku. He challenges him to a game of cat's cradle, though loses terribly. Hayate and Hinagiku later spend the next day together after school after running into each other in town, she accepts Hayate's apology for yesterday and accidentally says that she expected the person who wrote her letter to be Hayate which causes her to run away in embarrassment. She then falls of a tree trying to save a cat but falls but is caught by Hayate, who gives her the stuffed rabbit she wanted.

Izumi, Miki, and Risa invite Hayate and Nagi to their "You-To-Be" Motion Picture Research school club where they film and gather funny movies and laugh at them. Nagi shows interest in the club and Hayate believes it's an opportunity to get Nagi to break her hikikomori habits. They are shown example videos which happen to be Hayate's embarrassing moments with voice overs. Hayate snaps and destroys the club's equipment and media just before Superintendent Kirika appears for her annual club investigation. It turns out the club is on the verge of being shut down and the trio were planning to use the video of Hayate as a means of keeping the club alive. As a backup plan, they promise Kirika new footage of Hayate jumping off the clock tower. With the club saved and Hayate and Nagi as new members, the club decides to hold a normal story competition. Risa tells the first story and soon the mic is passed around to even non-club members.

Nagi and Ayumu compete together in the 4256th High School Girls Ultra Quiz tournament, though are each looking forward to the possibility of winning different prizes; Nagi wants the trophy for its resemblance to Hayate, and Ayumu wants the all-you-can-eat ticket to a restaurant so she can go out with Hayate. During the tournament, Nagi and Ayumu have trouble cooperating, though manage to end up winning the tournament in the end. Ayumu uses the all-you-can-eat ticket to invite Nagi, and Hayate to go out and eat together.

Nagi is planning a celebration party for Hayate for graduating, though gets him to stay out of the mansion for a while by giving him the task of retrieving a small box carrying an item she bought off the Internet. While out, Hayate is offered 150,000,000 yen by a national escort service in order to recruit him into their business and so that he can pay off his debt to Nagi. While thinking this offer over, he loses the box and has to go halfway around the world in order to retrieve it, though by the time he gets back to the mansion its already dark out. Hayate is very grateful to Nagi for the party, and the item he retrieved which was intended for him, and turned out to be a small pocket watch. Hayate later turns down the offer from the escort service, and it turns out that Nagi's grandfather set up the offer in order to test Hayate's loyalty.

During Golden Week, Hayate, Nagi, and Maria take a trip to an island in the Aegean Sea. Nagi still does not like to go outside much, though she gives in to Hayate after he sulks. While out the next day, Nagi's hat is blown away by the wind, and when Hayate goes to retrieve it, he falls into a time slip and arrives many years previous when Nagi was living on the island. After he realizes what is going on, he discovers she is being targeted by the Mafia, and he ends up protecting her from them, ultimately winning; Hayate realizes that the reason he was sent back was to save Nagi. Hayate had promised Nagi in the past to watch the stars together at the beach, but when they go at sunset, Nagi's hat once again is blown away and Hayate goes through another time slip back to the present. This caused Nagi to remember Hayate in the past as a liar who disappeared on her and took her hat with him. Back in the present, Hayate gives Nagi back her hat and the two gaze at the starry night sky together.