Nagi Sanzenin is a character from the Hayate no Gotoku! manga and anime series. She 13 years old, biracial, and the only heir to the Sanzenin fortune. She is short-tempered, spoiled, immature, but kind and cute. She has an otaku-level hobby with manga, anime and video games, and draws her own manga, which is called "Millennium Legend: Magical Destroy" whose main protagonist is a magical girl named Britney (ブリトニー Buritonī). Many of the characters in the anime think that Britney is very ugly and that Nagi's manga sucked. Nagi has a large crush on Hayate, and she thinks that Hayate loves her since they first met. She sometimes tries to make him take an interest in her in many ways, and sometimes, she succeeds. She has successfully kissed Hayate 2 times in total. She gets really jealous when Hayate makes some good statements on other girls, and then punches his face. However, Hayate never understands why Nagi is mad at him (until the final episode of Can't Take My Eyes Off You).
Nagi's only surviving family is her grandfather, whom she greatly dislikes. She regards Maria as an older sister figure, but gets ultimately jealous when Hayate is out with Maria or is alone with her. Nagi's mother, Yukariko, is shown in volume 12 of the manga. She cares for her family and friends, but she doesn't want to show her concern directly, she usually shows her concern with "formal words". Because of her pampered existence, she lacks any worldly knowledge and is even incapable of looking after herself. Nagi is mortally afraid of the dark (due to an incident with Isumi), and so shares her bed with Maria at night. Since going outside is very dangerous because of her status, Nagi favors staying at home, not liking company in general. Hayate managed to convince Nagi that sports is good for her body, and she is able to get into 2nd place on the Hakuō freestyle marathon due to Hayate's absorbing training and her huge amount of love for him.
Nagi is very selfish, but mostly what she likes to do is not so good for her future. She is hard to control; even Maria who has lots of talents can't control her. But Hayate, her average educated and insensitive butler, who saved her from the kidnappers and the mafia, and police chase that occurred from the race that she loses from him, is able to convince her to go to school, do exercise, have many friends, etc. He helps Nagi to be a better person. While Hayate always reminded her to go outside and gather experiences on the outside world, she always thought that will be boring or she will always get lost and risk being kidnapped. Maria always states to her that without Hayate she will always get lost or in danger. Nagi spent most of her younger years living outside Japan. Because of her family's wealth, she became the prime target of criminal organizations. Nagi disliked being a target and spent most of her days indoors playing video games and watching TV and hence slowly becoming a hikikomori. She begins to go to school more often after Hayate transfers to her school. Despite her laziness, Nagi is a highly intelligent student. She skipped grades and is currently in the first year of high school and in the same class as Hayate. Another funny thing about Nagi is that she always forgets the everyday life of an ordinary person.
"Nagi" means "windless" or "calmness", which seems to be the contrast of Hayate, which means "gust of wind" or "squall".
In Shimoda, Nagi decided to take Hayate and Maria on a trip to visit a mysterious meteorite that seems to enhance growth, along with other special powers. Nagi decided to help the alien, Maya, to find its misplaced spaceship. Nagi and Maya find the spaceship at the Saginomiya's place. Nagi accidentally boards on the spaceship, luckily Hayate saves her. When Maya sends Hayate and Nagi home, Hayate encounters Nagi's mother, Yukariko, in a dream and finds out the reason why Nagi comes to Shimoda every year is to remember the anniversary of her mother's death.
On the other hand, in Episode 52, during Golden Week, Nagi, Hayate, and Maria travel to Mykonos Island. Hayate got summoned back to the past when he jumped into the sky to get Nagi's hat back. At that time, Nagi feels uncomfortable going outside, because the mafia is after her. However, Hayate manages to defeat the Sicilian mafia but he made a few holes on Nagi's hat. Nagi doesn't mind and said that the holes are proof that Hayate saved her life. After this incident, Nagi falls for Hayate even more because he has vowed to protect her in the past, present and future. Both Nagis (The one in the present and the one from the past) fall for Hayate deeply. During Hayate's struggle to make a choice whether to destroy the King's Jewel to save Athena, Nagi sensed Hayate's dilemma and decided to destroy the king's jewel out of her own accord so that Hayate could now protect her truly, and not her fortune. She came across Athena on the last day of Golden Week. After coming back from Golden Week trip, Nagi was forced to leave her mansion due to her forfeiting her inheritance after she destroyed the King's Jewel. Later Nagi, Hayate, and Maria stayed at Yukariko's Violet Mansion and started new life.
Nagi trying to sell her doujinshi to the public. Nagi went to show her hard work to Ashibashi-sensei but was shocked to realize her hard work was not good enough. Later, Chiharu tried to cheer her up by taking her to a Doujinshi covention. After making a bet to sell out her doujinshi at the last convention, Nagi gets help from both Chiharu, Hayate, and Kayura in coming out with ideas to create her own doujinshi compare to Ruka her rival. In chapter 328, Hayate invites Ruka over to accompany Nagi in drawing her own doujinshi. After the Comisun event, Nagi decide to make a comeback at the Tokyo Big Sight to where the biggest doujinshi competition will be held there. Believing that having supernatural experiences will help create a concept manuscript for a new manga, Nagi takes an itinerary to Kyoto, but later got lost on the empty streets of Hokkaido until she's found late at night by Dr. Kurosu. Nagi determined to win the competition for Hayate's sake when Ruka confronts her feelings for him. As Nagi's manga, "30 Days of Soul Burning", is being sold and read, she soon realize what she had sincerely desire in her life.