AnimeEditNagi Dài Artai is the ruler of the Principality of Artai. His right-hand man is Major Sergay Wáng of the Artai military. He enjoys teasing and flirting with Mashiro.
Unlike his Mai-HiME incarnation, this Nagi is outright malevolent and more of a warmonger and mastermind. In the beginning of the series, he tries to take over Windbloom Kingdom, first by proposing marriage to Queen Mashiro Blan de Windbloom (who rejects him) and then by force, with the help of the Schwarz organization and its public figure, John Smith.
When Smith retrieves data regarding the lost technology of the Earth colonists, he uses it to mass-produce a new generation of SLAVE units. After Schwarz takes over Windbloom with the help of the SLAVEs and a powerful cannon secretly installed on top of the rebuilt Windbloom Castle, Nagi organizes a staged "liberation", moving the Artai army into the city and putting it under his authoritarian control. Despite the outrageous nature of his actions, other nations do not intervene, as Artai is technically not violating any international laws. Meanwhile, Nagi is shown to have been in possession of the Ultimate Black Diamond GEM all along, which he uses to forge a contract with Nina Wáng, his new Meister Otome.
As the series progresses, it is revealed that Nagi is interested in the hidden technology stored beneath Garderobe Academy and Windbloom Castle. More specifically, Schwarz's research provides him with his own Otome unit, the Valkyries, and unlocking the long-lost Harmonium provides him with a weapon of mass destruction to dictate his will to foreign nations. After an impressive demonstration of the Harmonium's power, some nations do side with Artai, while others — most prominently Aries and Zipang — forge an alliance against Nagi, organized by Natsuki Kruger, the refugee Headmaster of Garderobe. A war erupts.
During the final battle, Natsuki and her Otome retake Garderobe and defeat Nagi's SLAVEs, while Arika Yumemiya puts an end to the Valkyries and later defeats Nina and renders the Harmonium useless; Mikotothen destroys the Harmonium. Despite rapidly losing on all fronts, Nagi tries to retain self-control; he explains that he wanted to throw the society back to the way it was before the advent of the Otome system, which he considers an ineficient substitute for war.
Nagi tries to run away, but is arrested by Chie Hallard and put into servitude to Mikoto the cat goddess along with the remaining Schwarz cultists. At the end of episode 26 he is seen trying to escape, but Mikoto bashes him with her staff, rendering him unconscious, and then drags him back to the chain of prisoners.
He also appears briefly in episodes 1 and 2 of Mai-Otome Zwei imprisoned, the first with a non speaking role, and in the second with a small part at the end of the episode where he suggests that information on the mysterious entity petrifying the Otome may be located in Artai. He is also seen in the last episode of Mai-Otome Zwei looking at a Book called "Nagi's Smile Diary" XI or XII, suggesting that he's been keeping diaries since he's been in prison.
In the manga Nagi is initially Nina's master and appears to be just as malevolent as his anime counterpart, having destroyed several countries for the misbehavior of one or two representatives. He also treats Otome, including Nina, with contempt that prompts a violent reaction out of Mashiro's male impostor, whom he is initially engaged to. However, he shows a kinder side and sacrifices himself to save Mashiro from Mikoto and urges Nina to fight with Mashiro. He claims, at the time of his death, that he had truly fallen in love with the male Mashiro - the revelation of his gender did not change this. Nagi also has a younger sister, Arashi Daí Artai, whose goals are similar to those of her older brother, and stars in a spin off manga of her own.
AnimeEditNagi makes his first appearance in the first episode of the Mai-HiME anime commenting that another HiME has arrived. He is first seen conversing with Mashiro Kazahana and Fumi Himeno after the latter two meet Mai Tokiha for the first time and he comments on Mai's HiME status. Later in the same episode, Nagi appears to Mai and Natsuki Kuga, and implies that her brother Takumi Tokiha is threatened by an Orphan, and as Mai strives to protect him, Nagi introduces her to her HiME powers and her Child, Kagutsuchi.
Nagi is an observer to the awakening of several more HiMEs, and also acts as a sort of referee to prevent fights between them. It is revealed that he is behind the Orphan attacks on Fuka Academy; both Fumi and Mashiro (who mentions Nagi being part of the First District) are aware of this, as is Natsuki, who reluctantly leaves him alone as long as he discloses the Orphans' directions.
Soon, however, Orphans of another kind come into play, catching even Nagi by surprise as he is not aware who sends them. The other Orphan master turns out to be Alyssa Searrs, an artificial HiME created by the Searrs Foundation with the goal of disposing of all other HiME. Nagi, still staying in the shadows, aids the other HiME in their quest to protect Fuka Academy from the Searrs Foundation.
After Searrs's plans are foiled and Alyssa is killed, Nagi appears before the "HiME Rangers", newly formed byMidori Sugiura to more efficiently protect Fuka against Orphans, and tells them that Orphans will not be appearing any more — instead, the HiME will have to fight each other's Childs until only one HiME retains her powers, as part of the HiME Carnival that occurs every 300 years,. He is later revealed — along with the First District — to be a servant to the Obsidian Lord, the ancient power behind the HiME Carnival, and that Nagi himself witnessed previous HiME Carnivals, which would make him several centuries old.
As the HiME Star descends to Fuka Academy, Nagi guides Mai (the only HiME remaining by that point, bar Mikoto Minagi) through Valhalla's Gate to the HiME star and to her final showdown with Mikoto and the Obsidian Lord. He then tries to prevent Miyu Greer from following Mai's footsteps into the hall with the pillars representing HiME, but his attempt to stop is Miyu unsuccessful and, to his shock, she unleashes her ultimate "Platinum" mode, shattering the crystal in which Mashiro's real body is encased and freeing her.
After the Obsidian Lord is defeated, Nagi's eyes glow yellow and he screams, clutching his head. When he regains consciousness, he laments his failure to prevent the HiME from cheating their fate. He is last seen conversing with Mashiro and Fumi; he comments that the destruction of the HiME Star made the future less certain. Nagi and Mashiro then decide to "go back where they belong" and disappear in a pitch black room behind a massive gate, which then closes behind them, leaving Fumi behind.
Nagi, as portrayed in Mai-HiME, is a trickster. He likes eavesdropping, standing or sitting on high ground (especially tree branches), and suddenly and unexpectedly appearing before other characters to deliver vague bits of information. He wears a white shirt and usually has his hands put in the pockets on his trousers. He also often carries a book or balances it on his head; in the final episode, just before disappearing, he gives the book to Fumi, and it is revealed to bear the words "Fuka Academy" on its cover.
In the Mai-HiME manga, Nagi is a much more malevolent figure than in the anime. From his first appearance, it is clear that he is the one directing the Orphans against the HiME. Nagi appears out of nowhere as in the anime, often carrying a book, but his actions and words are openly malicious. He maintains secrecy about his own allegiance and purpose and violently attacks anyone who tries to disclose the truth. He is apparently killed by Miyu Grear in volume 3, when he had almost escaped an ambush organized by the combined HiME teams and Mashiro. However, this was proven to be false, as multiple copies of him appeared inside the Obsidian Palace, and continued to multiply themselves even during battle. They all fought Miyu, who continued to fight them even after most of her weapons had been used up, till the HiME star collapsed upon itself and became a unique Child.
- Nagi's seiyuu Akira Ishida also voiced Athrun Zala from the Gundam SEED series.