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The main male protagonist 16-year-old butler of the Sanzenin family, Hayate Ayasaki has had to work to support his parents' bad habits since the age of nine, always moving from job to job, before he was found out to be underage. The experience gained does mean, however, that of all the characters, he possesses the most extensive practical knowledge he has is of how the world operates. Hayate's dad has refused to get employed, while his mother is a compulsive gambler, and the whereabouts of Hayate's older brother, Ikusa, are unknown. These events led to their bankruptcy—they abandon Hayate attempt to sell his organs to the Yakuza to ease their financial burdens on Christmas Eve, a debt of 156,804,000 yen. With not many choices left to him, Hayate conspired to kidnap someone to get ransom money. He found a girl, Nagi Sanzenin, and told her that he would kidnap her. However, Nagi mistook his words for his confession of love, so he was later employed as Nagi's new butler. In the beginning of the story, he often mentioned Nello and Patrasche from the novel A Dog of Flanders, and compared his miserable situation to the characters' life.
As a butler, Hayate is capable of all aspects of housework and can even play the violin, but it is his ability in repelling attacks from almost anything, including butlers of other families (despite his bad luck) that makes him a "combat butler". He once demonstrated a skilled use of fire-arms (capable of wielding an MG3 single-handedly) and is essentially invincible with physical prowess far surpassing any normal human being. Hayate once parried a sword thrust easily with just two fingers, and in Volume 8, revealed that doing over 350 one-finger push-ups is part of his daily routine since he was little, among other displays of his strength. At the end of Volume 6, Hayate manages to create an ultimate technique called Hayate no Gotoku (like the wind).
Hayate sees Nagi as a child, and has a crush on the more mature Maria. However, he gets really annoyed when Nagi and Maria force him to wear female clothing. In chapter 156, it is revealed that he sleeps three hours a day: studying until 2am, waking up at 5am (the reason that he gets up at 5 is that he thinks it would be unwise to wake up after Maria has done so).
In addition to looking poor and seedy, Hayate can also appear to be extremely feminine. He has a girlish face and is good at housework such as cooking and cleaning, which are usually thought to be work for women; he is also very modest and sensitive, all of which contribute to others' perception of him as feminine. This has led to him being forced to wear girls' clothing or cosplay in feminine outfits such as nekomimi, a maid and so on. In episode 36 of the anime, he cosplays as Belldandy from Ah! My Goddess. Later on, this female alter-ego is given a name: Hermione Ayasaki (綾崎 ハーマイオニー Ayasaki Hamaioni?). He has been forced to cross-dress at other times, but he is not referred to by his alter-ego's name on these occasions.
Although he possesses a wide range of skills, his empathy is very poor, to the point where he often hurts the people around him because he doesn't understand their feelings towards him. He is truly a handicap on dealing with his admirers' feelings towards him. However, Hayate's attitude towards a relationship is actually very positive. Athena taught him that he must be economically strong if he wants to date with a girl.
On the other hand, he often unintentionally embarrasses others by reacting wildly at very simple requests. Such as in volume 8, when Hinagiku asks if he wants to take a bath and he thinks that she wants to take a bath together. This may be because of his innocent personality, which often leads him into trouble with other people. It seems that he also has a crush on her. In the following episode (Season 2 Episode 7), Hayate and Hinagiku created a spark when they both accidentally touched each other's hands. They both blush, and Hinagiku rushed out of the house to buy some ice cream because she can't face her crush due to embarrassment. It seems that their feelings for each other have increased. He also has a slight interest in Ayumu after Ayumu hugged Hayate on Valentine's Day, and their feelings have increased after Ayumu gave some suggestions to Hayate on what he should buy for Hinagiku, Maria, and Nagi on Episode 10 of Season 2. He also gave some cookies as a present for Ayumu on White Day because Ayumu had saved Nagi from being killed by the mafia on Episode 15 of Season 2.
He had a girlfriend named Athena, who was responsible for teaching him cleaning and swordsmanship, as well as for building his strong body. They had a falling out after his parents pawned an "engagement" ring she gave him. In chapter 239, after being asked by Hinagiku how he feels about Athena, Hayate describes Athena as "Not like the others," and ultimately tells Hinagiku that he is in love with Athena. Following her advice to meet her, he goes to her mansion and confronts Machina, who nearly kills him and steals his 'King's Stone' before Athena brings him in and treats him. After these events he rescues Athena and they express their feelings one another as they still love each other. At the end he tells her that she is the one he loves but he comes to deciding he must first protect Nagi. Hayate would go back to Mykonos for one more day of vacation before returning to Japan.
Back in Japan, Hayate had to deal with the problem of Nagi losing the inheritance and thus the mansion. In the end, Hayate met Klaus who showed him an old house, "Violet Mansion". Klaus received the house from Yukariko Sanzenin decades ago and said it was only proper that the house be returned to its rightful owner, Yukariko's daughter, Nagi. Having settled in their new home, Hayate (in Hermione form) met Ruka Suirenji an idol help carried her to where she was scheduled to perform when attacked by a robot control by Yozora, with Ruka still thinking that Hayate is a girl. After that, Athena appeared again in chapter 300, to ask Hayate where his brother was. She told him that she would appear again, and that he should act like they had never met before. She appeared again as a child, with no memories, only that her mission was to find the owner of the Shirosakura, Hinagiku, to help restore her powers. She also stated that Hayate was the one she trusted most. Recently Hayate, Linn, Tama discovered a mystery room partitioned in the storage room. After Isumi disables the barrier, Hayate discovers that the room holds the same coffin he saw in the Royal Garden 10 years ago. Shortly after that Yozora shows up and burns the coffin whilst battling Isumi briefly. He proceeds to intervene when Yozora threatened Athena but was countered effortlessly by her. He later buys groceries for a Welcome Party for the Violet Mansion tenants.
Currently there are a total of 10 people that are in love with Hayate, many of which he has no clue to their true feelings due to his dense nature. They are: Hinagiku, Ayumu, Ruka, Izumi, Isumi, Maria, Nagi, Sakuya, Athena and Kotetsu (Homosexual). However, Hayate has only shown interest in Hinagiku, Maria, Ayumu, Athena, and Ruka.